Documentation/gpu: split up mm, kms and kms-helpers from internals

Make the documents more manageable.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/be992e56eb8442d6e03b52444df5a42525085718.1466506505.git.jani.nikula@intel.com

Documentation/gpu/drm-internals.rst

@@ -40,7 +40,7 @@ Driver Information
 ------------------
 
 Driver Features
-^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~
 
 Drivers inform the DRM core about their requirements and supported
 features by setting appropriate flags in the driver_features field.
@@ -96,7 +96,7 @@ DRIVER_ATOMIC
     modeset objects with driver specific properties.
 
 Major, Minor and Patchlevel
-^^^^^^^^^^^^^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 int major; int minor; int patchlevel;
 The DRM core identifies driver versions by a major, minor and patch
@@ -114,7 +114,7 @@ return an error. Otherwise the driver's set_version() method will be
 called with the requested version.
 
 Name, Description and Date
-^^^^^^^^^^^^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 char \*name; char \*desc; char \*date;
 The driver name is printed to the kernel log at initialization time,
@@ -144,7 +144,7 @@ Driver Load
 -----------
 
 IRQ Registration
-^^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~~
 
 The DRM core tries to facilitate IRQ handler registration and
 unregistration by providing :c:func:`drm_irq_install()` and
@@ -198,7 +198,7 @@ registration of the IRQs, and clear it to 0 after unregistering the
 IRQs.
 
 Memory Manager Initialization
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Every DRM driver requires a memory manager which must be initialized at
 load time. DRM currently contains two memory managers, the Translation
@@ -207,7 +207,7 @@ document describes the use of the GEM memory manager only. See ? for
 details.
 
 Miscellaneous Device Configuration
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Another task that may be necessary for PCI devices during configuration
 is mapping the video BIOS. On many devices, the VBIOS describes device
@@ -236,1373 +236,6 @@ drivers.
 .. kernel-doc:: drivers/gpu/drm/drm_platform.c
    :export:
 
-Memory management
-=================
-
-Modern Linux systems require large amount of graphics memory to store
-frame buffers, textures, vertices and other graphics-related data. Given
-the very dynamic nature of many of that data, managing graphics memory
-efficiently is thus crucial for the graphics stack and plays a central
-role in the DRM infrastructure.
-
-The DRM core includes two memory managers, namely Translation Table Maps
-(TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
-manager to be developed and tried to be a one-size-fits-them all
-solution. It provides a single userspace API to accommodate the need of
-all hardware, supporting both Unified Memory Architecture (UMA) devices
-and devices with dedicated video RAM (i.e. most discrete video cards).
-This resulted in a large, complex piece of code that turned out to be
-hard to use for driver development.
-
-GEM started as an Intel-sponsored project in reaction to TTM's
-complexity. Its design philosophy is completely different: instead of
-providing a solution to every graphics memory-related problems, GEM
-identified common code between drivers and created a support library to
-share it. GEM has simpler initialization and execution requirements than
-TTM, but has no video RAM management capabilities and is thus limited to
-UMA devices.
-
-The Translation Table Manager (TTM)
------------------------------------
-
-TTM design background and information belongs here.
-
-TTM initialization
-^^^^^^^^^^^^^^^^^^
-
-    **Warning**
-
-    This section is outdated.
-
-Drivers wishing to support TTM must fill out a drm_bo_driver
-structure. The structure contains several fields with function pointers
-for initializing the TTM, allocating and freeing memory, waiting for
-command completion and fence synchronization, and memory migration. See
-the radeon_ttm.c file for an example of usage.
-
-The ttm_global_reference structure is made up of several fields:
-
-::
-
-              struct ttm_global_reference {
-                      enum ttm_global_types global_type;
-                      size_t size;
-                      void *object;
-                      int (*init) (struct ttm_global_reference *);
-                      void (*release) (struct ttm_global_reference *);
-              };
-
-
-There should be one global reference structure for your memory manager
-as a whole, and there will be others for each object created by the
-memory manager at runtime. Your global TTM should have a type of
-TTM_GLOBAL_TTM_MEM. The size field for the global object should be
-sizeof(struct ttm_mem_global), and the init and release hooks should
-point at your driver-specific init and release routines, which probably
-eventually call ttm_mem_global_init and ttm_mem_global_release,
-respectively.
-
-Once your global TTM accounting structure is set up and initialized by
-calling ttm_global_item_ref() on it, you need to create a buffer
-object TTM to provide a pool for buffer object allocation by clients and
-the kernel itself. The type of this object should be
-TTM_GLOBAL_TTM_BO, and its size should be sizeof(struct
-ttm_bo_global). Again, driver-specific init and release functions may
-be provided, likely eventually calling ttm_bo_global_init() and
-ttm_bo_global_release(), respectively. Also, like the previous
-object, ttm_global_item_ref() is used to create an initial reference
-count for the TTM, which will call your initialization function.
-
-The Graphics Execution Manager (GEM)
-------------------------------------
-
-The GEM design approach has resulted in a memory manager that doesn't
-provide full coverage of all (or even all common) use cases in its
-userspace or kernel API. GEM exposes a set of standard memory-related
-operations to userspace and a set of helper functions to drivers, and
-let drivers implement hardware-specific operations with their own
-private API.
-
-The GEM userspace API is described in the `GEM - the Graphics Execution
-Manager <http://lwn.net/Articles/283798/>`__ article on LWN. While
-slightly outdated, the document provides a good overview of the GEM API
-principles. Buffer allocation and read and write operations, described
-as part of the common GEM API, are currently implemented using
-driver-specific ioctls.
-
-GEM is data-agnostic. It manages abstract buffer objects without knowing
-what individual buffers contain. APIs that require knowledge of buffer
-contents or purpose, such as buffer allocation or synchronization
-primitives, are thus outside of the scope of GEM and must be implemented
-using driver-specific ioctls.
-
-On a fundamental level, GEM involves several operations:
-
--  Memory allocation and freeing
--  Command execution
--  Aperture management at command execution time
-
-Buffer object allocation is relatively straightforward and largely
-provided by Linux's shmem layer, which provides memory to back each
-object.
-
-Device-specific operations, such as command execution, pinning, buffer
-read & write, mapping, and domain ownership transfers are left to
-driver-specific ioctls.
-
-GEM Initialization
-^^^^^^^^^^^^^^^^^^
-
-Drivers that use GEM must set the DRIVER_GEM bit in the struct
-:c:type:`struct drm_driver <drm_driver>` driver_features
-field. The DRM core will then automatically initialize the GEM core
-before calling the load operation. Behind the scene, this will create a
-DRM Memory Manager object which provides an address space pool for
-object allocation.
-
-In a KMS configuration, drivers need to allocate and initialize a
-command ring buffer following core GEM initialization if required by the
-hardware. UMA devices usually have what is called a "stolen" memory
-region, which provides space for the initial framebuffer and large,
-contiguous memory regions required by the device. This space is
-typically not managed by GEM, and must be initialized separately into
-its own DRM MM object.
-
-GEM Objects Creation
-^^^^^^^^^^^^^^^^^^^^
-
-GEM splits creation of GEM objects and allocation of the memory that
-backs them in two distinct operations.
-
-GEM objects are represented by an instance of struct :c:type:`struct
-drm_gem_object <drm_gem_object>`. Drivers usually need to
-extend GEM objects with private information and thus create a
-driver-specific GEM object structure type that embeds an instance of
-struct :c:type:`struct drm_gem_object <drm_gem_object>`.
-
-To create a GEM object, a driver allocates memory for an instance of its
-specific GEM object type and initializes the embedded struct
-:c:type:`struct drm_gem_object <drm_gem_object>` with a call
-to :c:func:`drm_gem_object_init()`. The function takes a pointer
-to the DRM device, a pointer to the GEM object and the buffer object
-size in bytes.
-
-GEM uses shmem to allocate anonymous pageable memory.
-:c:func:`drm_gem_object_init()` will create an shmfs file of the
-requested size and store it into the struct :c:type:`struct
-drm_gem_object <drm_gem_object>` filp field. The memory is
-used as either main storage for the object when the graphics hardware
-uses system memory directly or as a backing store otherwise.
-
-Drivers are responsible for the actual physical pages allocation by
-calling :c:func:`shmem_read_mapping_page_gfp()` for each page.
-Note that they can decide to allocate pages when initializing the GEM
-object, or to delay allocation until the memory is needed (for instance
-when a page fault occurs as a result of a userspace memory access or
-when the driver needs to start a DMA transfer involving the memory).
-
-Anonymous pageable memory allocation is not always desired, for instance
-when the hardware requires physically contiguous system memory as is
-often the case in embedded devices. Drivers can create GEM objects with
-no shmfs backing (called private GEM objects) by initializing them with
-a call to :c:func:`drm_gem_private_object_init()` instead of
-:c:func:`drm_gem_object_init()`. Storage for private GEM objects
-must be managed by drivers.
-
-GEM Objects Lifetime
-^^^^^^^^^^^^^^^^^^^^
-
-All GEM objects are reference-counted by the GEM core. References can be
-acquired and release by :c:func:`calling
-drm_gem_object_reference()` and
-:c:func:`drm_gem_object_unreference()` respectively. The caller
-must hold the :c:type:`struct drm_device <drm_device>`
-struct_mutex lock when calling
-:c:func:`drm_gem_object_reference()`. As a convenience, GEM
-provides :c:func:`drm_gem_object_unreference_unlocked()`
-functions that can be called without holding the lock.
-
-When the last reference to a GEM object is released the GEM core calls
-the :c:type:`struct drm_driver <drm_driver>` gem_free_object
-operation. That operation is mandatory for GEM-enabled drivers and must
-free the GEM object and all associated resources.
-
-void (\*gem_free_object) (struct drm_gem_object \*obj); Drivers are
-responsible for freeing all GEM object resources. This includes the
-resources created by the GEM core, which need to be released with
-:c:func:`drm_gem_object_release()`.
-
-GEM Objects Naming
-^^^^^^^^^^^^^^^^^^
-
-Communication between userspace and the kernel refers to GEM objects
-using local handles, global names or, more recently, file descriptors.
-All of those are 32-bit integer values; the usual Linux kernel limits
-apply to the file descriptors.
-
-GEM handles are local to a DRM file. Applications get a handle to a GEM
-object through a driver-specific ioctl, and can use that handle to refer
-to the GEM object in other standard or driver-specific ioctls. Closing a
-DRM file handle frees all its GEM handles and dereferences the
-associated GEM objects.
-
-To create a handle for a GEM object drivers call
-:c:func:`drm_gem_handle_create()`. The function takes a pointer
-to the DRM file and the GEM object and returns a locally unique handle.
-When the handle is no longer needed drivers delete it with a call to
-:c:func:`drm_gem_handle_delete()`. Finally the GEM object
-associated with a handle can be retrieved by a call to
-:c:func:`drm_gem_object_lookup()`.
-
-Handles don't take ownership of GEM objects, they only take a reference
-to the object that will be dropped when the handle is destroyed. To
-avoid leaking GEM objects, drivers must make sure they drop the
-reference(s) they own (such as the initial reference taken at object
-creation time) as appropriate, without any special consideration for the
-handle. For example, in the particular case of combined GEM object and
-handle creation in the implementation of the dumb_create operation,
-drivers must drop the initial reference to the GEM object before
-returning the handle.
-
-GEM names are similar in purpose to handles but are not local to DRM
-files. They can be passed between processes to reference a GEM object
-globally. Names can't be used directly to refer to objects in the DRM
-API, applications must convert handles to names and names to handles
-using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
-respectively. The conversion is handled by the DRM core without any
-driver-specific support.
-
-GEM also supports buffer sharing with dma-buf file descriptors through
-PRIME. GEM-based drivers must use the provided helpers functions to
-implement the exporting and importing correctly. See ?. Since sharing
-file descriptors is inherently more secure than the easily guessable and
-global GEM names it is the preferred buffer sharing mechanism. Sharing
-buffers through GEM names is only supported for legacy userspace.
-Furthermore PRIME also allows cross-device buffer sharing since it is
-based on dma-bufs.
-
-GEM Objects Mapping
-^^^^^^^^^^^^^^^^^^^
-
-Because mapping operations are fairly heavyweight GEM favours
-read/write-like access to buffers, implemented through driver-specific
-ioctls, over mapping buffers to userspace. However, when random access
-to the buffer is needed (to perform software rendering for instance),
-direct access to the object can be more efficient.
-
-The mmap system call can't be used directly to map GEM objects, as they
-don't have their own file handle. Two alternative methods currently
-co-exist to map GEM objects to userspace. The first method uses a
-driver-specific ioctl to perform the mapping operation, calling
-:c:func:`do_mmap()` under the hood. This is often considered
-dubious, seems to be discouraged for new GEM-enabled drivers, and will
-thus not be described here.
-
-The second method uses the mmap system call on the DRM file handle. void
-\*mmap(void \*addr, size_t length, int prot, int flags, int fd, off_t
-offset); DRM identifies the GEM object to be mapped by a fake offset
-passed through the mmap offset argument. Prior to being mapped, a GEM
-object must thus be associated with a fake offset. To do so, drivers
-must call :c:func:`drm_gem_create_mmap_offset()` on the object.
-
-Once allocated, the fake offset value must be passed to the application
-in a driver-specific way and can then be used as the mmap offset
-argument.
-
-The GEM core provides a helper method :c:func:`drm_gem_mmap()` to
-handle object mapping. The method can be set directly as the mmap file
-operation handler. It will look up the GEM object based on the offset
-value and set the VMA operations to the :c:type:`struct drm_driver
-<drm_driver>` gem_vm_ops field. Note that
-:c:func:`drm_gem_mmap()` doesn't map memory to userspace, but
-relies on the driver-provided fault handler to map pages individually.
-
-To use :c:func:`drm_gem_mmap()`, drivers must fill the struct
-:c:type:`struct drm_driver <drm_driver>` gem_vm_ops field
-with a pointer to VM operations.
-
-struct vm_operations_struct \*gem_vm_ops struct
-vm_operations_struct { void (\*open)(struct vm_area_struct \* area);
-void (\*close)(struct vm_area_struct \* area); int (\*fault)(struct
-vm_area_struct \*vma, struct vm_fault \*vmf); };
-
-The open and close operations must update the GEM object reference
-count. Drivers can use the :c:func:`drm_gem_vm_open()` and
-:c:func:`drm_gem_vm_close()` helper functions directly as open
-and close handlers.
-
-The fault operation handler is responsible for mapping individual pages
-to userspace when a page fault occurs. Depending on the memory
-allocation scheme, drivers can allocate pages at fault time, or can
-decide to allocate memory for the GEM object at the time the object is
-created.
-
-Drivers that want to map the GEM object upfront instead of handling page
-faults can implement their own mmap file operation handler.
-
-Memory Coherency
-^^^^^^^^^^^^^^^^
-
-When mapped to the device or used in a command buffer, backing pages for
-an object are flushed to memory and marked write combined so as to be
-coherent with the GPU. Likewise, if the CPU accesses an object after the
-GPU has finished rendering to the object, then the object must be made
-coherent with the CPU's view of memory, usually involving GPU cache
-flushing of various kinds. This core CPU<->GPU coherency management is
-provided by a device-specific ioctl, which evaluates an object's current
-domain and performs any necessary flushing or synchronization to put the
-object into the desired coherency domain (note that the object may be
-busy, i.e. an active render target; in that case, setting the domain
-blocks the client and waits for rendering to complete before performing
-any necessary flushing operations).
-
-Command Execution
-^^^^^^^^^^^^^^^^^
-
-Perhaps the most important GEM function for GPU devices is providing a
-command execution interface to clients. Client programs construct
-command buffers containing references to previously allocated memory
-objects, and then submit them to GEM. At that point, GEM takes care to
-bind all the objects into the GTT, execute the buffer, and provide
-necessary synchronization between clients accessing the same buffers.
-This often involves evicting some objects from the GTT and re-binding
-others (a fairly expensive operation), and providing relocation support
-which hides fixed GTT offsets from clients. Clients must take care not
-to submit command buffers that reference more objects than can fit in
-the GTT; otherwise, GEM will reject them and no rendering will occur.
-Similarly, if several objects in the buffer require fence registers to
-be allocated for correct rendering (e.g. 2D blits on pre-965 chips),
-care must be taken not to require more fence registers than are
-available to the client. Such resource management should be abstracted
-from the client in libdrm.
-
-GEM Function Reference
-----------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_gem.c
-   :export:
-
-.. kernel-doc:: include/drm/drm_gem.h
-   :internal:
-
-VMA Offset Manager
-------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c
-   :doc: vma offset manager
-
-.. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c
-   :export:
-
-.. kernel-doc:: include/drm/drm_vma_manager.h
-   :internal:
-
-PRIME Buffer Sharing
---------------------
-
-PRIME is the cross device buffer sharing framework in drm, originally
-created for the OPTIMUS range of multi-gpu platforms. To userspace PRIME
-buffers are dma-buf based file descriptors.
-
-Overview and Driver Interface
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Similar to GEM global names, PRIME file descriptors are also used to
-share buffer objects across processes. They offer additional security:
-as file descriptors must be explicitly sent over UNIX domain sockets to
-be shared between applications, they can't be guessed like the globally
-unique GEM names.
-
-Drivers that support the PRIME API must set the DRIVER_PRIME bit in the
-struct :c:type:`struct drm_driver <drm_driver>`
-driver_features field, and implement the prime_handle_to_fd and
-prime_fd_to_handle operations.
-
-int (\*prime_handle_to_fd)(struct drm_device \*dev, struct drm_file
-\*file_priv, uint32_t handle, uint32_t flags, int \*prime_fd); int
-(\*prime_fd_to_handle)(struct drm_device \*dev, struct drm_file
-\*file_priv, int prime_fd, uint32_t \*handle); Those two operations
-convert a handle to a PRIME file descriptor and vice versa. Drivers must
-use the kernel dma-buf buffer sharing framework to manage the PRIME file
-descriptors. Similar to the mode setting API PRIME is agnostic to the
-underlying buffer object manager, as long as handles are 32bit unsigned
-integers.
-
-While non-GEM drivers must implement the operations themselves, GEM
-drivers must use the :c:func:`drm_gem_prime_handle_to_fd()` and
-:c:func:`drm_gem_prime_fd_to_handle()` helper functions. Those
-helpers rely on the driver gem_prime_export and gem_prime_import
-operations to create a dma-buf instance from a GEM object (dma-buf
-exporter role) and to create a GEM object from a dma-buf instance
-(dma-buf importer role).
-
-struct dma_buf \* (\*gem_prime_export)(struct drm_device \*dev,
-struct drm_gem_object \*obj, int flags); struct drm_gem_object \*
-(\*gem_prime_import)(struct drm_device \*dev, struct dma_buf
-\*dma_buf); These two operations are mandatory for GEM drivers that
-support PRIME.
-
-PRIME Helper Functions
-^^^^^^^^^^^^^^^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_prime.c
-   :doc: PRIME Helpers
-
-PRIME Function References
--------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_prime.c
-   :export:
-
-DRM MM Range Allocator
-----------------------
-
-Overview
-^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_mm.c
-   :doc: Overview
-
-LRU Scan/Eviction Support
-^^^^^^^^^^^^^^^^^^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_mm.c
-   :doc: lru scan roaster
-
-DRM MM Range Allocator Function References
-------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_mm.c
-   :export:
-
-.. kernel-doc:: include/drm/drm_mm.h
-   :internal:
-
-CMA Helper Functions Reference
-------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
-   :doc: cma helpers
-
-.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
-   :export:
-
-.. kernel-doc:: include/drm/drm_gem_cma_helper.h
-   :internal:
-
-Mode Setting
-============
-
-Drivers must initialize the mode setting core by calling
-:c:func:`drm_mode_config_init()` on the DRM device. The function
-initializes the :c:type:`struct drm_device <drm_device>`
-mode_config field and never fails. Once done, mode configuration must
-be setup by initializing the following fields.
-
--  int min_width, min_height; int max_width, max_height;
-   Minimum and maximum width and height of the frame buffers in pixel
-   units.
-
--  struct drm_mode_config_funcs \*funcs;
-   Mode setting functions.
-
-Display Modes Function Reference
---------------------------------
-
-.. kernel-doc:: include/drm/drm_modes.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_modes.c
-   :export:
-
-Atomic Mode Setting Function Reference
---------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
-   :export:
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
-   :internal:
-
-Frame Buffer Abstraction
-------------------------
-
-Frame buffers are abstract memory objects that provide a source of
-pixels to scanout to a CRTC. Applications explicitly request the
-creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls
-and receive an opaque handle that can be passed to the KMS CRTC control,
-plane configuration and page flip functions.
-
-Frame buffers rely on the underneath memory manager for low-level memory
-operations. When creating a frame buffer applications pass a memory
-handle (or a list of memory handles for multi-planar formats) through
-the ``drm_mode_fb_cmd2`` argument. For drivers using GEM as their
-userspace buffer management interface this would be a GEM handle.
-Drivers are however free to use their own backing storage object
-handles, e.g. vmwgfx directly exposes special TTM handles to userspace
-and so expects TTM handles in the create ioctl and not GEM handles.
-
-The lifetime of a drm framebuffer is controlled with a reference count,
-drivers can grab additional references with
-:c:func:`drm_framebuffer_reference()`and drop them again with
-:c:func:`drm_framebuffer_unreference()`. For driver-private
-framebuffers for which the last reference is never dropped (e.g. for the
-fbdev framebuffer when the struct :c:type:`struct drm_framebuffer
-<drm_framebuffer>` is embedded into the fbdev helper struct)
-drivers can manually clean up a framebuffer at module unload time with
-:c:func:`drm_framebuffer_unregister_private()`.
-
-DRM Format Handling
--------------------
-
-.. kernel-doc:: include/drm/drm_fourcc.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_fourcc.c
-   :export:
-
-Dumb Buffer Objects
--------------------
-
-The KMS API doesn't standardize backing storage object creation and
-leaves it to driver-specific ioctls. Furthermore actually creating a
-buffer object even for GEM-based drivers is done through a
-driver-specific ioctl - GEM only has a common userspace interface for
-sharing and destroying objects. While not an issue for full-fledged
-graphics stacks that include device-specific userspace components (in
-libdrm for instance), this limit makes DRM-based early boot graphics
-unnecessarily complex.
-
-Dumb objects partly alleviate the problem by providing a standard API to
-create dumb buffers suitable for scanout, which can then be used to
-create KMS frame buffers.
-
-To support dumb objects drivers must implement the dumb_create,
-dumb_destroy and dumb_map_offset operations.
-
--  int (\*dumb_create)(struct drm_file \*file_priv, struct
-   drm_device \*dev, struct drm_mode_create_dumb \*args);
-   The dumb_create operation creates a driver object (GEM or TTM
-   handle) suitable for scanout based on the width, height and depth
-   from the struct :c:type:`struct drm_mode_create_dumb
-   <drm_mode_create_dumb>` argument. It fills the argument's
-   handle, pitch and size fields with a handle for the newly created
-   object and its line pitch and size in bytes.
-
--  int (\*dumb_destroy)(struct drm_file \*file_priv, struct
-   drm_device \*dev, uint32_t handle);
-   The dumb_destroy operation destroys a dumb object created by
-   dumb_create.
-
--  int (\*dumb_map_offset)(struct drm_file \*file_priv, struct
-   drm_device \*dev, uint32_t handle, uint64_t \*offset);
-   The dumb_map_offset operation associates an mmap fake offset with
-   the object given by the handle and returns it. Drivers must use the
-   :c:func:`drm_gem_create_mmap_offset()` function to associate
-   the fake offset as described in ?.
-
-Note that dumb objects may not be used for gpu acceleration, as has been
-attempted on some ARM embedded platforms. Such drivers really must have
-a hardware-specific ioctl to allocate suitable buffer objects.
-
-Output Polling
---------------
-
-void (\*output_poll_changed)(struct drm_device \*dev);
-This operation notifies the driver that the status of one or more
-connectors has changed. Drivers that use the fb helper can just call the
-:c:func:`drm_fb_helper_hotplug_event()` function to handle this
-operation.
-
-KMS Initialization and Cleanup
-==============================
-
-A KMS device is abstracted and exposed as a set of planes, CRTCs,
-encoders and connectors. KMS drivers must thus create and initialize all
-those objects at load time after initializing mode setting.
-
-CRTCs (:c:type:`struct drm_crtc <drm_crtc>`)
---------------------------------------------
-
-A CRTC is an abstraction representing a part of the chip that contains a
-pointer to a scanout buffer. Therefore, the number of CRTCs available
-determines how many independent scanout buffers can be active at any
-given time. The CRTC structure contains several fields to support this:
-a pointer to some video memory (abstracted as a frame buffer object), a
-display mode, and an (x, y) offset into the video memory to support
-panning or configurations where one piece of video memory spans multiple
-CRTCs.
-
-CRTC Initialization
-^^^^^^^^^^^^^^^^^^^
-
-A KMS device must create and register at least one struct
-:c:type:`struct drm_crtc <drm_crtc>` instance. The instance is
-allocated and zeroed by the driver, possibly as part of a larger
-structure, and registered with a call to :c:func:`drm_crtc_init()`
-with a pointer to CRTC functions.
-
-Planes (:c:type:`struct drm_plane <drm_plane>`)
------------------------------------------------
-
-A plane represents an image source that can be blended with or overlayed
-on top of a CRTC during the scanout process. Planes are associated with
-a frame buffer to crop a portion of the image memory (source) and
-optionally scale it to a destination size. The result is then blended
-with or overlayed on top of a CRTC.
-
-The DRM core recognizes three types of planes:
-
--  DRM_PLANE_TYPE_PRIMARY represents a "main" plane for a CRTC.
-   Primary planes are the planes operated upon by CRTC modesetting and
-   flipping operations described in the page_flip hook in
-   :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`.
--  DRM_PLANE_TYPE_CURSOR represents a "cursor" plane for a CRTC.
-   Cursor planes are the planes operated upon by the
-   DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2 ioctls.
--  DRM_PLANE_TYPE_OVERLAY represents all non-primary, non-cursor
-   planes. Some drivers refer to these types of planes as "sprites"
-   internally.
-
-For compatibility with legacy userspace, only overlay planes are made
-available to userspace by default. Userspace clients may set the
-DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate
-that they wish to receive a universal plane list containing all plane
-types.
-
-Plane Initialization
-^^^^^^^^^^^^^^^^^^^^
-
-To create a plane, a KMS drivers allocates and zeroes an instances of
-:c:type:`struct drm_plane <drm_plane>` (possibly as part of a
-larger structure) and registers it with a call to
-:c:func:`drm_universal_plane_init()`. The function takes a
-bitmask of the CRTCs that can be associated with the plane, a pointer to
-the plane functions, a list of format supported formats, and the type of
-plane (primary, cursor, or overlay) being initialized.
-
-Cursor and overlay planes are optional. All drivers should provide one
-primary plane per CRTC (although this requirement may change in the
-future); drivers that do not wish to provide special handling for
-primary planes may make use of the helper functions described in ? to
-create and register a primary plane with standard capabilities.
-
-Encoders (:c:type:`struct drm_encoder <drm_encoder>`)
------------------------------------------------------
-
-An encoder takes pixel data from a CRTC and converts it to a format
-suitable for any attached connectors. On some devices, it may be
-possible to have a CRTC send data to more than one encoder. In that
-case, both encoders would receive data from the same scanout buffer,
-resulting in a "cloned" display configuration across the connectors
-attached to each encoder.
-
-Encoder Initialization
-^^^^^^^^^^^^^^^^^^^^^^
-
-As for CRTCs, a KMS driver must create, initialize and register at least
-one :c:type:`struct drm_encoder <drm_encoder>` instance. The
-instance is allocated and zeroed by the driver, possibly as part of a
-larger structure.
-
-Drivers must initialize the :c:type:`struct drm_encoder
-<drm_encoder>` possible_crtcs and possible_clones fields before
-registering the encoder. Both fields are bitmasks of respectively the
-CRTCs that the encoder can be connected to, and sibling encoders
-candidate for cloning.
-
-After being initialized, the encoder must be registered with a call to
-:c:func:`drm_encoder_init()`. The function takes a pointer to the
-encoder functions and an encoder type. Supported types are
-
--  DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
--  DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
--  DRM_MODE_ENCODER_LVDS for display panels
--  DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video,
-   Component, SCART)
--  DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
-
-Encoders must be attached to a CRTC to be used. DRM drivers leave
-encoders unattached at initialization time. Applications (or the fbdev
-compatibility layer when implemented) are responsible for attaching the
-encoders they want to use to a CRTC.
-
-Connectors (:c:type:`struct drm_connector <drm_connector>`)
------------------------------------------------------------
-
-A connector is the final destination for pixel data on a device, and
-usually connects directly to an external display device like a monitor
-or laptop panel. A connector can only be attached to one encoder at a
-time. The connector is also the structure where information about the
-attached display is kept, so it contains fields for display data, EDID
-data, DPMS & connection status, and information about modes supported on
-the attached displays.
-
-Connector Initialization
-^^^^^^^^^^^^^^^^^^^^^^^^
-
-Finally a KMS driver must create, initialize, register and attach at
-least one :c:type:`struct drm_connector <drm_connector>`
-instance. The instance is created as other KMS objects and initialized
-by setting the following fields.
-
-interlace_allowed
-    Whether the connector can handle interlaced modes.
-
-doublescan_allowed
-    Whether the connector can handle doublescan.
-
-display_info
-    Display information is filled from EDID information when a display
-    is detected. For non hot-pluggable displays such as flat panels in
-    embedded systems, the driver should initialize the
-    display_info.width_mm and display_info.height_mm fields with the
-    physical size of the display.
-
-polled
-    Connector polling mode, a combination of
-
-    DRM_CONNECTOR_POLL_HPD
-        The connector generates hotplug events and doesn't need to be
-        periodically polled. The CONNECT and DISCONNECT flags must not
-        be set together with the HPD flag.
-
-    DRM_CONNECTOR_POLL_CONNECT
-        Periodically poll the connector for connection.
-
-    DRM_CONNECTOR_POLL_DISCONNECT
-        Periodically poll the connector for disconnection.
-
-    Set to 0 for connectors that don't support connection status
-    discovery.
-
-The connector is then registered with a call to
-:c:func:`drm_connector_init()` with a pointer to the connector
-functions and a connector type, and exposed through sysfs with a call to
-:c:func:`drm_connector_register()`.
-
-Supported connector types are
-
--  DRM_MODE_CONNECTOR_VGA
--  DRM_MODE_CONNECTOR_DVII
--  DRM_MODE_CONNECTOR_DVID
--  DRM_MODE_CONNECTOR_DVIA
--  DRM_MODE_CONNECTOR_Composite
--  DRM_MODE_CONNECTOR_SVIDEO
--  DRM_MODE_CONNECTOR_LVDS
--  DRM_MODE_CONNECTOR_Component
--  DRM_MODE_CONNECTOR_9PinDIN
--  DRM_MODE_CONNECTOR_DisplayPort
--  DRM_MODE_CONNECTOR_HDMIA
--  DRM_MODE_CONNECTOR_HDMIB
--  DRM_MODE_CONNECTOR_TV
--  DRM_MODE_CONNECTOR_eDP
--  DRM_MODE_CONNECTOR_VIRTUAL
-
-Connectors must be attached to an encoder to be used. For devices that
-map connectors to encoders 1:1, the connector should be attached at
-initialization time with a call to
-:c:func:`drm_mode_connector_attach_encoder()`. The driver must
-also set the :c:type:`struct drm_connector <drm_connector>`
-encoder field to point to the attached encoder.
-
-Finally, drivers must initialize the connectors state change detection
-with a call to :c:func:`drm_kms_helper_poll_init()`. If at least
-one connector is pollable but can't generate hotplug interrupts
-(indicated by the DRM_CONNECTOR_POLL_CONNECT and
-DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
-automatically be queued to periodically poll for changes. Connectors
-that can generate hotplug interrupts must be marked with the
-DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
-call :c:func:`drm_helper_hpd_irq_event()`. The function will
-queue a delayed work to check the state of all connectors, but no
-periodic polling will be done.
-
-Connector Operations
-^^^^^^^^^^^^^^^^^^^^
-
-    **Note**
-
-    Unless otherwise state, all operations are mandatory.
-
-DPMS
-''''
-
-void (\*dpms)(struct drm_connector \*connector, int mode);
-The DPMS operation sets the power state of a connector. The mode
-argument is one of
-
--  DRM_MODE_DPMS_ON
-
--  DRM_MODE_DPMS_STANDBY
-
--  DRM_MODE_DPMS_SUSPEND
-
--  DRM_MODE_DPMS_OFF
-
-In all but DPMS_ON mode the encoder to which the connector is attached
-should put the display in low-power mode by driving its signals
-appropriately. If more than one connector is attached to the encoder
-care should be taken not to change the power state of other displays as
-a side effect. Low-power mode should be propagated to the encoders and
-CRTCs when all related connectors are put in low-power mode.
-
-Modes
-'''''
-
-int (\*fill_modes)(struct drm_connector \*connector, uint32_t
-max_width, uint32_t max_height);
-Fill the mode list with all supported modes for the connector. If the
-``max_width`` and ``max_height`` arguments are non-zero, the
-implementation must ignore all modes wider than ``max_width`` or higher
-than ``max_height``.
-
-The connector must also fill in this operation its display_info
-width_mm and height_mm fields with the connected display physical size
-in millimeters. The fields should be set to 0 if the value isn't known
-or is not applicable (for instance for projector devices).
-
-Connection Status
-'''''''''''''''''
-
-The connection status is updated through polling or hotplug events when
-supported (see ?). The status value is reported to userspace through
-ioctls and must not be used inside the driver, as it only gets
-initialized by a call to :c:func:`drm_mode_getconnector()` from
-userspace.
-
-enum drm_connector_status (\*detect)(struct drm_connector
-\*connector, bool force);
-Check to see if anything is attached to the connector. The ``force``
-parameter is set to false whilst polling or to true when checking the
-connector due to user request. ``force`` can be used by the driver to
-avoid expensive, destructive operations during automated probing.
-
-Return connector_status_connected if something is connected to the
-connector, connector_status_disconnected if nothing is connected and
-connector_status_unknown if the connection state isn't known.
-
-Drivers should only return connector_status_connected if the
-connection status has really been probed as connected. Connectors that
-can't detect the connection status, or failed connection status probes,
-should return connector_status_unknown.
-
-Cleanup
--------
-
-The DRM core manages its objects' lifetime. When an object is not needed
-anymore the core calls its destroy function, which must clean up and
-free every resource allocated for the object. Every
-:c:func:`drm_\*_init()` call must be matched with a corresponding
-:c:func:`drm_\*_cleanup()` call to cleanup CRTCs
-(:c:func:`drm_crtc_cleanup()`), planes
-(:c:func:`drm_plane_cleanup()`), encoders
-(:c:func:`drm_encoder_cleanup()`) and connectors
-(:c:func:`drm_connector_cleanup()`). Furthermore, connectors that
-have been added to sysfs must be removed by a call to
-:c:func:`drm_connector_unregister()` before calling
-:c:func:`drm_connector_cleanup()`.
-
-Connectors state change detection must be cleanup up with a call to
-:c:func:`drm_kms_helper_poll_fini()`.
-
-Output discovery and initialization example
--------------------------------------------
-
-::
-
-    void intel_crt_init(struct drm_device *dev)
-    {
-        struct drm_connector *connector;
-        struct intel_output *intel_output;
-
-        intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
-        if (!intel_output)
-            return;
-
-        connector = &intel_output->base;
-        drm_connector_init(dev, &intel_output->base,
-                   &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
-
-        drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
-                 DRM_MODE_ENCODER_DAC);
-
-        drm_mode_connector_attach_encoder(&intel_output->base,
-                          &intel_output->enc);
-
-        /* Set up the DDC bus. */
-        intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
-        if (!intel_output->ddc_bus) {
-            dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
-                   "failed.\n");
-            return;
-        }
-
-        intel_output->type = INTEL_OUTPUT_ANALOG;
-        connector->interlace_allowed = 0;
-        connector->doublescan_allowed = 0;
-
-        drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
-        drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
-
-        drm_connector_register(connector);
-    }
-
-In the example above (taken from the i915 driver), a CRTC, connector and
-encoder combination is created. A device-specific i2c bus is also
-created for fetching EDID data and performing monitor detection. Once
-the process is complete, the new connector is registered with sysfs to
-make its properties available to applications.
-
-KMS API Functions
------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
-   :export:
-
-KMS Data Structures
--------------------
-
-.. kernel-doc:: include/drm/drm_crtc.h
-   :internal:
-
-KMS Locking
------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
-   :doc: kms locking
-
-.. kernel-doc:: include/drm/drm_modeset_lock.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
-   :export:
-
-Mode Setting Helper Functions
-=============================
-
-The plane, CRTC, encoder and connector functions provided by the drivers
-implement the DRM API. They're called by the DRM core and ioctl handlers
-to handle device state changes and configuration request. As
-implementing those functions often requires logic not specific to
-drivers, mid-layer helper functions are available to avoid duplicating
-boilerplate code.
-
-The DRM core contains one mid-layer implementation. The mid-layer
-provides implementations of several plane, CRTC, encoder and connector
-functions (called from the top of the mid-layer) that pre-process
-requests and call lower-level functions provided by the driver (at the
-bottom of the mid-layer). For instance, the
-:c:func:`drm_crtc_helper_set_config()` function can be used to
-fill the :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`
-set_config field. When called, it will split the set_config operation
-in smaller, simpler operations and call the driver to handle them.
-
-To use the mid-layer, drivers call
-:c:func:`drm_crtc_helper_add()`,
-:c:func:`drm_encoder_helper_add()` and
-:c:func:`drm_connector_helper_add()` functions to install their
-mid-layer bottom operations handlers, and fill the :c:type:`struct
-drm_crtc_funcs <drm_crtc_funcs>`, :c:type:`struct
-drm_encoder_funcs <drm_encoder_funcs>` and :c:type:`struct
-drm_connector_funcs <drm_connector_funcs>` structures with
-pointers to the mid-layer top API functions. Installing the mid-layer
-bottom operation handlers is best done right after registering the
-corresponding KMS object.
-
-The mid-layer is not split between CRTC, encoder and connector
-operations. To use it, a driver must provide bottom functions for all of
-the three KMS entities.
-
-Atomic Modeset Helper Functions Reference
------------------------------------------
-
-Overview
-^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
-   :doc: overview
-
-Implementing Asynchronous Atomic Commit
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
-   :doc: implementing nonblocking commit
-
-Atomic State Reset and Initialization
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
-   :doc: atomic state reset and initialization
-
-.. kernel-doc:: include/drm/drm_atomic_helper.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
-   :export:
-
-Modeset Helper Reference for Common Vtables
--------------------------------------------
-
-.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h
-   :internal:
-
-.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h
-   :doc: overview
-
-Legacy CRTC/Modeset Helper Functions Reference
-----------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
-   :export:
-
-.. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
-   :doc: overview
-
-Output Probing Helper Functions Reference
------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c
-   :doc: output probing helper overview
-
-.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c
-   :export:
-
-fbdev Helper Functions Reference
---------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_fb_helper.c
-   :doc: fbdev helpers
-
-.. kernel-doc:: drivers/gpu/drm/drm_fb_helper.c
-   :export:
-
-.. kernel-doc:: include/drm/drm_fb_helper.h
-   :internal:
-
-Framebuffer CMA Helper Functions Reference
-------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_fb_cma_helper.c
-   :doc: framebuffer cma helper functions
-
-.. kernel-doc:: drivers/gpu/drm/drm_fb_cma_helper.c
-   :export:
-
-Display Port Helper Functions Reference
----------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_dp_helper.c
-   :doc: dp helpers
-
-.. kernel-doc:: include/drm/drm_dp_helper.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_dp_helper.c
-   :export:
-
-Display Port Dual Mode Adaptor Helper Functions Reference
----------------------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_dp_dual_mode_helper.c
-   :doc: dp dual mode helpers
-
-.. kernel-doc:: include/drm/drm_dp_dual_mode_helper.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_dp_dual_mode_helper.c
-   :export:
-
-Display Port MST Helper Functions Reference
--------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
-   :doc: dp mst helper
-
-.. kernel-doc:: include/drm/drm_dp_mst_helper.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
-   :export:
-
-MIPI DSI Helper Functions Reference
------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c
-   :doc: dsi helpers
-
-.. kernel-doc:: include/drm/drm_mipi_dsi.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c
-   :export:
-
-EDID Helper Functions Reference
--------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_edid.c
-   :export:
-
-Rectangle Utilities Reference
------------------------------
-
-.. kernel-doc:: include/drm/drm_rect.h
-   :doc: rect utils
-
-.. kernel-doc:: include/drm/drm_rect.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_rect.c
-   :export:
-
-Flip-work Helper Reference
---------------------------
-
-.. kernel-doc:: include/drm/drm_flip_work.h
-   :doc: flip utils
-
-.. kernel-doc:: include/drm/drm_flip_work.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_flip_work.c
-   :export:
-
-HDMI Infoframes Helper Reference
---------------------------------
-
-Strictly speaking this is not a DRM helper library but generally useable
-by any driver interfacing with HDMI outputs like v4l or alsa drivers.
-But it nicely fits into the overall topic of mode setting helper
-libraries and hence is also included here.
-
-.. kernel-doc:: include/linux/hdmi.h
-   :internal:
-
-.. kernel-doc:: drivers/video/hdmi.c
-   :export:
-
-Plane Helper Reference
-----------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c
-   :export:
-
-.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c
-   :doc: overview
-
-Tile group
-----------
-
-.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
-   :doc: Tile group
-
-Bridges
--------
-
-Overview
-^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
-   :doc: overview
-
-Default bridge callback sequence
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
-   :doc: bridge callbacks
-
-.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
-   :export:
-
-Panel Helper Reference
-----------------------
-
-.. kernel-doc:: include/drm/drm_panel.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_panel.c
-   :export:
-
-.. kernel-doc:: drivers/gpu/drm/drm_panel.c
-   :doc: drm panel
-
-Simple KMS Helper Reference
----------------------------
-
-.. kernel-doc:: include/drm/drm_simple_kms_helper.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c
-   :export:
-
-.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c
-   :doc: overview
-
-KMS Properties
-==============
-
-Drivers may need to expose additional parameters to applications than
-those described in the previous sections. KMS supports attaching
-properties to CRTCs, connectors and planes and offers a userspace API to
-list, get and set the property values.
-
-Properties are identified by a name that uniquely defines the property
-purpose, and store an associated value. For all property types except
-blob properties the value is a 64-bit unsigned integer.
-
-KMS differentiates between properties and property instances. Drivers
-first create properties and then create and associate individual
-instances of those properties to objects. A property can be instantiated
-multiple times and associated with different objects. Values are stored
-in property instances, and all other property information are stored in
-the property and shared between all instances of the property.
-
-Every property is created with a type that influences how the KMS core
-handles the property. Supported property types are
-
-DRM_MODE_PROP_RANGE
-    Range properties report their minimum and maximum admissible values.
-    The KMS core verifies that values set by application fit in that
-    range.
-
-DRM_MODE_PROP_ENUM
-    Enumerated properties take a numerical value that ranges from 0 to
-    the number of enumerated values defined by the property minus one,
-    and associate a free-formed string name to each value. Applications
-    can retrieve the list of defined value-name pairs and use the
-    numerical value to get and set property instance values.
-
-DRM_MODE_PROP_BITMASK
-    Bitmask properties are enumeration properties that additionally
-    restrict all enumerated values to the 0..63 range. Bitmask property
-    instance values combine one or more of the enumerated bits defined
-    by the property.
-
-DRM_MODE_PROP_BLOB
-    Blob properties store a binary blob without any format restriction.
-    The binary blobs are created as KMS standalone objects, and blob
-    property instance values store the ID of their associated blob
-    object.
-
-    Blob properties are only used for the connector EDID property and
-    cannot be created by drivers.
-
-To create a property drivers call one of the following functions
-depending on the property type. All property creation functions take
-property flags and name, as well as type-specific arguments.
-
--  struct drm_property \*drm_property_create_range(struct
-   drm_device \*dev, int flags, const char \*name, uint64_t min,
-   uint64_t max);
-   Create a range property with the given minimum and maximum values.
-
--  struct drm_property \*drm_property_create_enum(struct drm_device
-   \*dev, int flags, const char \*name, const struct
-   drm_prop_enum_list \*props, int num_values);
-   Create an enumerated property. The ``props`` argument points to an
-   array of ``num_values`` value-name pairs.
-
--  struct drm_property \*drm_property_create_bitmask(struct
-   drm_device \*dev, int flags, const char \*name, const struct
-   drm_prop_enum_list \*props, int num_values);
-   Create a bitmask property. The ``props`` argument points to an array
-   of ``num_values`` value-name pairs.
-
-Properties can additionally be created as immutable, in which case they
-will be read-only for applications but can be modified by the driver. To
-create an immutable property drivers must set the
-DRM_MODE_PROP_IMMUTABLE flag at property creation time.
-
-When no array of value-name pairs is readily available at property
-creation time for enumerated or range properties, drivers can create the
-property using the :c:func:`drm_property_create()` function and
-manually add enumeration value-name pairs by calling the
-:c:func:`drm_property_add_enum()` function. Care must be taken to
-properly specify the property type through the ``flags`` argument.
-
-After creating properties drivers can attach property instances to CRTC,
-connector and plane objects by calling the
-:c:func:`drm_object_attach_property()`. The function takes a
-pointer to the target object, a pointer to the previously created
-property and an initial instance value.
-
-Existing KMS Properties
------------------------
-
-The following table gives description of drm properties exposed by
-various modules/drivers.
-
-.. csv-table::
-   :header-rows: 1
-   :file: kms-properties.csv
-
-Vertical Blanking
-=================
-
-Vertical blanking plays a major role in graphics rendering. To achieve
-tear-free display, users must synchronize page flips and/or rendering to
-vertical blanking. The DRM API offers ioctls to perform page flips
-synchronized to vertical blanking and wait for vertical blanking.
-
-The DRM core handles most of the vertical blanking management logic,
-which involves filtering out spurious interrupts, keeping race-free
-blanking counters, coping with counter wrap-around and resets and
-keeping use counts. It relies on the driver to generate vertical
-blanking interrupts and optionally provide a hardware vertical blanking
-counter. Drivers must implement the following operations.
-
--  int (\*enable_vblank) (struct drm_device \*dev, int crtc); void
-   (\*disable_vblank) (struct drm_device \*dev, int crtc);
-   Enable or disable vertical blanking interrupts for the given CRTC.
-
--  u32 (\*get_vblank_counter) (struct drm_device \*dev, int crtc);
-   Retrieve the value of the vertical blanking counter for the given
-   CRTC. If the hardware maintains a vertical blanking counter its value
-   should be returned. Otherwise drivers can use the
-   :c:func:`drm_vblank_count()` helper function to handle this
-   operation.
-
-Drivers must initialize the vertical blanking handling core with a call
-to :c:func:`drm_vblank_init()` in their load operation.
-
-Vertical blanking interrupts can be enabled by the DRM core or by
-drivers themselves (for instance to handle page flipping operations).
-The DRM core maintains a vertical blanking use count to ensure that the
-interrupts are not disabled while a user still needs them. To increment
-the use count, drivers call :c:func:`drm_vblank_get()`. Upon
-return vertical blanking interrupts are guaranteed to be enabled.
-
-To decrement the use count drivers call
-:c:func:`drm_vblank_put()`. Only when the use count drops to zero
-will the DRM core disable the vertical blanking interrupts after a delay
-by scheduling a timer. The delay is accessible through the
-vblankoffdelay module parameter or the ``drm_vblank_offdelay`` global
-variable and expressed in milliseconds. Its default value is 5000 ms.
-Zero means never disable, and a negative value means disable
-immediately. Drivers may override the behaviour by setting the
-:c:type:`struct drm_device <drm_device>`
-vblank_disable_immediate flag, which when set causes vblank interrupts
-to be disabled immediately regardless of the drm_vblank_offdelay
-value. The flag should only be set if there's a properly working
-hardware vblank counter present.
-
-When a vertical blanking interrupt occurs drivers only need to call the
-:c:func:`drm_handle_vblank()` function to account for the
-interrupt.
-
-Resources allocated by :c:func:`drm_vblank_init()` must be freed
-with a call to :c:func:`drm_vblank_cleanup()` in the driver unload
-operation handler.
-
-Vertical Blanking and Interrupt Handling Functions Reference
-------------------------------------------------------------
-
-.. kernel-doc:: drivers/gpu/drm/drm_irq.c
-   :export:
-
-.. kernel-doc:: include/drm/drmP.h
-   :functions: drm_crtc_vblank_waitqueue
-
 Open/Close, File Operations and IOCTLs
 ======================================
 

Documentation/gpu/drm-kms-helpers.rst

+=============================
+Mode Setting Helper Functions
+=============================
+
+The plane, CRTC, encoder and connector functions provided by the drivers
+implement the DRM API. They're called by the DRM core and ioctl handlers
+to handle device state changes and configuration request. As
+implementing those functions often requires logic not specific to
+drivers, mid-layer helper functions are available to avoid duplicating
+boilerplate code.
+
+The DRM core contains one mid-layer implementation. The mid-layer
+provides implementations of several plane, CRTC, encoder and connector
+functions (called from the top of the mid-layer) that pre-process
+requests and call lower-level functions provided by the driver (at the
+bottom of the mid-layer). For instance, the
+:c:func:`drm_crtc_helper_set_config()` function can be used to
+fill the :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`
+set_config field. When called, it will split the set_config operation
+in smaller, simpler operations and call the driver to handle them.
+
+To use the mid-layer, drivers call
+:c:func:`drm_crtc_helper_add()`,
+:c:func:`drm_encoder_helper_add()` and
+:c:func:`drm_connector_helper_add()` functions to install their
+mid-layer bottom operations handlers, and fill the :c:type:`struct
+drm_crtc_funcs <drm_crtc_funcs>`, :c:type:`struct
+drm_encoder_funcs <drm_encoder_funcs>` and :c:type:`struct
+drm_connector_funcs <drm_connector_funcs>` structures with
+pointers to the mid-layer top API functions. Installing the mid-layer
+bottom operation handlers is best done right after registering the
+corresponding KMS object.
+
+The mid-layer is not split between CRTC, encoder and connector
+operations. To use it, a driver must provide bottom functions for all of
+the three KMS entities.
+
+Atomic Modeset Helper Functions Reference
+=========================================
+
+Overview
+--------
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+   :doc: overview
+
+Implementing Asynchronous Atomic Commit
+---------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+   :doc: implementing nonblocking commit
+
+Atomic State Reset and Initialization
+-------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+   :doc: atomic state reset and initialization
+
+.. kernel-doc:: include/drm/drm_atomic_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
+   :export:
+
+Modeset Helper Reference for Common Vtables
+===========================================
+
+.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h
+   :internal:
+
+.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h
+   :doc: overview
+
+Legacy CRTC/Modeset Helper Functions Reference
+==============================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
+   :export:
+
+.. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
+   :doc: overview
+
+Output Probing Helper Functions Reference
+=========================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c
+   :doc: output probing helper overview
+
+.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c
+   :export:
+
+fbdev Helper Functions Reference
+================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_fb_helper.c
+   :doc: fbdev helpers
+
+.. kernel-doc:: drivers/gpu/drm/drm_fb_helper.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_fb_helper.h
+   :internal:
+
+Framebuffer CMA Helper Functions Reference
+==========================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_fb_cma_helper.c
+   :doc: framebuffer cma helper functions
+
+.. kernel-doc:: drivers/gpu/drm/drm_fb_cma_helper.c
+   :export:
+
+Display Port Helper Functions Reference
+=======================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_helper.c
+   :doc: dp helpers
+
+.. kernel-doc:: include/drm/drm_dp_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_helper.c
+   :export:
+
+Display Port Dual Mode Adaptor Helper Functions Reference
+=========================================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_dual_mode_helper.c
+   :doc: dp dual mode helpers
+
+.. kernel-doc:: include/drm/drm_dp_dual_mode_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_dual_mode_helper.c
+   :export:
+
+Display Port MST Helper Functions Reference
+===========================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
+   :doc: dp mst helper
+
+.. kernel-doc:: include/drm/drm_dp_mst_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
+   :export:
+
+MIPI DSI Helper Functions Reference
+===================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c
+   :doc: dsi helpers
+
+.. kernel-doc:: include/drm/drm_mipi_dsi.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c
+   :export:
+
+EDID Helper Functions Reference
+===============================
+
+.. kernel-doc:: drivers/gpu/drm/drm_edid.c
+   :export:
+
+Rectangle Utilities Reference
+=============================
+
+.. kernel-doc:: include/drm/drm_rect.h
+   :doc: rect utils
+
+.. kernel-doc:: include/drm/drm_rect.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_rect.c
+   :export:
+
+Flip-work Helper Reference
+==========================
+
+.. kernel-doc:: include/drm/drm_flip_work.h
+   :doc: flip utils
+
+.. kernel-doc:: include/drm/drm_flip_work.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_flip_work.c
+   :export:
+
+HDMI Infoframes Helper Reference
+================================
+
+Strictly speaking this is not a DRM helper library but generally useable
+by any driver interfacing with HDMI outputs like v4l or alsa drivers.
+But it nicely fits into the overall topic of mode setting helper
+libraries and hence is also included here.
+
+.. kernel-doc:: include/linux/hdmi.h
+   :internal:
+
+.. kernel-doc:: drivers/video/hdmi.c
+   :export:
+
+Plane Helper Reference
+======================
+
+.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c
+   :export:
+
+.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c
+   :doc: overview
+
+Tile group
+----------
+
+.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
+   :doc: Tile group
+
+Bridges
+=======
+
+Overview
+--------
+
+.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
+   :doc: overview
+
+Default bridge callback sequence
+--------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
+   :doc: bridge callbacks
+
+.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
+   :export:
+
+Panel Helper Reference
+======================
+
+.. kernel-doc:: include/drm/drm_panel.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_panel.c
+   :export:
+
+.. kernel-doc:: drivers/gpu/drm/drm_panel.c
+   :doc: drm panel
+
+Simple KMS Helper Reference
+===========================
+
+.. kernel-doc:: include/drm/drm_simple_kms_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c
+   :export:
+
+.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c
+   :doc: overview

Documentation/gpu/drm-kms.rst

+=========================
+Kernel Mode Setting (KMS)
+=========================
+
+Mode Setting
+============
+
+Drivers must initialize the mode setting core by calling
+:c:func:`drm_mode_config_init()` on the DRM device. The function
+initializes the :c:type:`struct drm_device <drm_device>`
+mode_config field and never fails. Once done, mode configuration must
+be setup by initializing the following fields.
+
+-  int min_width, min_height; int max_width, max_height;
+   Minimum and maximum width and height of the frame buffers in pixel
+   units.
+
+-  struct drm_mode_config_funcs \*funcs;
+   Mode setting functions.
+
+Display Modes Function Reference
+--------------------------------
+
+.. kernel-doc:: include/drm/drm_modes.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_modes.c
+   :export:
+
+Atomic Mode Setting Function Reference
+--------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
+   :export:
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
+   :internal:
+
+Frame Buffer Abstraction
+------------------------
+
+Frame buffers are abstract memory objects that provide a source of
+pixels to scanout to a CRTC. Applications explicitly request the
+creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls
+and receive an opaque handle that can be passed to the KMS CRTC control,
+plane configuration and page flip functions.
+
+Frame buffers rely on the underneath memory manager for low-level memory
+operations. When creating a frame buffer applications pass a memory
+handle (or a list of memory handles for multi-planar formats) through
+the ``drm_mode_fb_cmd2`` argument. For drivers using GEM as their
+userspace buffer management interface this would be a GEM handle.
+Drivers are however free to use their own backing storage object
+handles, e.g. vmwgfx directly exposes special TTM handles to userspace
+and so expects TTM handles in the create ioctl and not GEM handles.
+
+The lifetime of a drm framebuffer is controlled with a reference count,
+drivers can grab additional references with
+:c:func:`drm_framebuffer_reference()`and drop them again with
+:c:func:`drm_framebuffer_unreference()`. For driver-private
+framebuffers for which the last reference is never dropped (e.g. for the
+fbdev framebuffer when the struct :c:type:`struct drm_framebuffer
+<drm_framebuffer>` is embedded into the fbdev helper struct)
+drivers can manually clean up a framebuffer at module unload time with
+:c:func:`drm_framebuffer_unregister_private()`.
+
+DRM Format Handling
+-------------------
+
+.. kernel-doc:: include/drm/drm_fourcc.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_fourcc.c
+   :export:
+
+Dumb Buffer Objects
+-------------------
+
+The KMS API doesn't standardize backing storage object creation and
+leaves it to driver-specific ioctls. Furthermore actually creating a
+buffer object even for GEM-based drivers is done through a
+driver-specific ioctl - GEM only has a common userspace interface for
+sharing and destroying objects. While not an issue for full-fledged
+graphics stacks that include device-specific userspace components (in
+libdrm for instance), this limit makes DRM-based early boot graphics
+unnecessarily complex.
+
+Dumb objects partly alleviate the problem by providing a standard API to
+create dumb buffers suitable for scanout, which can then be used to
+create KMS frame buffers.
+
+To support dumb objects drivers must implement the dumb_create,
+dumb_destroy and dumb_map_offset operations.
+
+-  int (\*dumb_create)(struct drm_file \*file_priv, struct
+   drm_device \*dev, struct drm_mode_create_dumb \*args);
+   The dumb_create operation creates a driver object (GEM or TTM
+   handle) suitable for scanout based on the width, height and depth
+   from the struct :c:type:`struct drm_mode_create_dumb
+   <drm_mode_create_dumb>` argument. It fills the argument's
+   handle, pitch and size fields with a handle for the newly created
+   object and its line pitch and size in bytes.
+
+-  int (\*dumb_destroy)(struct drm_file \*file_priv, struct
+   drm_device \*dev, uint32_t handle);
+   The dumb_destroy operation destroys a dumb object created by
+   dumb_create.
+
+-  int (\*dumb_map_offset)(struct drm_file \*file_priv, struct
+   drm_device \*dev, uint32_t handle, uint64_t \*offset);
+   The dumb_map_offset operation associates an mmap fake offset with
+   the object given by the handle and returns it. Drivers must use the
+   :c:func:`drm_gem_create_mmap_offset()` function to associate
+   the fake offset as described in ?.
+
+Note that dumb objects may not be used for gpu acceleration, as has been
+attempted on some ARM embedded platforms. Such drivers really must have
+a hardware-specific ioctl to allocate suitable buffer objects.
+
+Output Polling
+--------------
+
+void (\*output_poll_changed)(struct drm_device \*dev);
+This operation notifies the driver that the status of one or more
+connectors has changed. Drivers that use the fb helper can just call the
+:c:func:`drm_fb_helper_hotplug_event()` function to handle this
+operation.
+
+KMS Initialization and Cleanup
+==============================
+
+A KMS device is abstracted and exposed as a set of planes, CRTCs,
+encoders and connectors. KMS drivers must thus create and initialize all
+those objects at load time after initializing mode setting.
+
+CRTCs (:c:type:`struct drm_crtc <drm_crtc>`)
+--------------------------------------------
+
+A CRTC is an abstraction representing a part of the chip that contains a
+pointer to a scanout buffer. Therefore, the number of CRTCs available
+determines how many independent scanout buffers can be active at any
+given time. The CRTC structure contains several fields to support this:
+a pointer to some video memory (abstracted as a frame buffer object), a
+display mode, and an (x, y) offset into the video memory to support
+panning or configurations where one piece of video memory spans multiple
+CRTCs.
+
+CRTC Initialization
+~~~~~~~~~~~~~~~~~~~
+
+A KMS device must create and register at least one struct
+:c:type:`struct drm_crtc <drm_crtc>` instance. The instance is
+allocated and zeroed by the driver, possibly as part of a larger
+structure, and registered with a call to :c:func:`drm_crtc_init()`
+with a pointer to CRTC functions.
+
+Planes (:c:type:`struct drm_plane <drm_plane>`)
+-----------------------------------------------
+
+A plane represents an image source that can be blended with or overlayed
+on top of a CRTC during the scanout process. Planes are associated with
+a frame buffer to crop a portion of the image memory (source) and
+optionally scale it to a destination size. The result is then blended
+with or overlayed on top of a CRTC.
+
+The DRM core recognizes three types of planes:
+
+-  DRM_PLANE_TYPE_PRIMARY represents a "main" plane for a CRTC.
+   Primary planes are the planes operated upon by CRTC modesetting and
+   flipping operations described in the page_flip hook in
+   :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`.
+-  DRM_PLANE_TYPE_CURSOR represents a "cursor" plane for a CRTC.
+   Cursor planes are the planes operated upon by the
+   DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2 ioctls.
+-  DRM_PLANE_TYPE_OVERLAY represents all non-primary, non-cursor
+   planes. Some drivers refer to these types of planes as "sprites"
+   internally.
+
+For compatibility with legacy userspace, only overlay planes are made
+available to userspace by default. Userspace clients may set the
+DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate
+that they wish to receive a universal plane list containing all plane
+types.
+
+Plane Initialization
+~~~~~~~~~~~~~~~~~~~~
+
+To create a plane, a KMS drivers allocates and zeroes an instances of
+:c:type:`struct drm_plane <drm_plane>` (possibly as part of a
+larger structure) and registers it with a call to
+:c:func:`drm_universal_plane_init()`. The function takes a
+bitmask of the CRTCs that can be associated with the plane, a pointer to
+the plane functions, a list of format supported formats, and the type of
+plane (primary, cursor, or overlay) being initialized.
+
+Cursor and overlay planes are optional. All drivers should provide one
+primary plane per CRTC (although this requirement may change in the
+future); drivers that do not wish to provide special handling for
+primary planes may make use of the helper functions described in ? to
+create and register a primary plane with standard capabilities.
+
+Encoders (:c:type:`struct drm_encoder <drm_encoder>`)
+-----------------------------------------------------
+
+An encoder takes pixel data from a CRTC and converts it to a format
+suitable for any attached connectors. On some devices, it may be
+possible to have a CRTC send data to more than one encoder. In that
+case, both encoders would receive data from the same scanout buffer,
+resulting in a "cloned" display configuration across the connectors
+attached to each encoder.
+
+Encoder Initialization
+~~~~~~~~~~~~~~~~~~~~~~
+
+As for CRTCs, a KMS driver must create, initialize and register at least
+one :c:type:`struct drm_encoder <drm_encoder>` instance. The
+instance is allocated and zeroed by the driver, possibly as part of a
+larger structure.
+
+Drivers must initialize the :c:type:`struct drm_encoder
+<drm_encoder>` possible_crtcs and possible_clones fields before
+registering the encoder. Both fields are bitmasks of respectively the
+CRTCs that the encoder can be connected to, and sibling encoders
+candidate for cloning.
+
+After being initialized, the encoder must be registered with a call to
+:c:func:`drm_encoder_init()`. The function takes a pointer to the
+encoder functions and an encoder type. Supported types are
+
+-  DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
+-  DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
+-  DRM_MODE_ENCODER_LVDS for display panels
+-  DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video,
+   Component, SCART)
+-  DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
+
+Encoders must be attached to a CRTC to be used. DRM drivers leave
+encoders unattached at initialization time. Applications (or the fbdev
+compatibility layer when implemented) are responsible for attaching the
+encoders they want to use to a CRTC.
+
+Connectors (:c:type:`struct drm_connector <drm_connector>`)
+-----------------------------------------------------------
+
+A connector is the final destination for pixel data on a device, and
+usually connects directly to an external display device like a monitor
+or laptop panel. A connector can only be attached to one encoder at a
+time. The connector is also the structure where information about the
+attached display is kept, so it contains fields for display data, EDID
+data, DPMS & connection status, and information about modes supported on
+the attached displays.
+
+Connector Initialization
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Finally a KMS driver must create, initialize, register and attach at
+least one :c:type:`struct drm_connector <drm_connector>`
+instance. The instance is created as other KMS objects and initialized
+by setting the following fields.
+
+interlace_allowed
+    Whether the connector can handle interlaced modes.
+
+doublescan_allowed
+    Whether the connector can handle doublescan.
+
+display_info
+    Display information is filled from EDID information when a display
+    is detected. For non hot-pluggable displays such as flat panels in
+    embedded systems, the driver should initialize the
+    display_info.width_mm and display_info.height_mm fields with the
+    physical size of the display.
+
+polled
+    Connector polling mode, a combination of
+
+    DRM_CONNECTOR_POLL_HPD
+        The connector generates hotplug events and doesn't need to be
+        periodically polled. The CONNECT and DISCONNECT flags must not
+        be set together with the HPD flag.
+
+    DRM_CONNECTOR_POLL_CONNECT
+        Periodically poll the connector for connection.
+
+    DRM_CONNECTOR_POLL_DISCONNECT
+        Periodically poll the connector for disconnection.
+
+    Set to 0 for connectors that don't support connection status
+    discovery.
+
+The connector is then registered with a call to
+:c:func:`drm_connector_init()` with a pointer to the connector
+functions and a connector type, and exposed through sysfs with a call to
+:c:func:`drm_connector_register()`.
+
+Supported connector types are
+
+-  DRM_MODE_CONNECTOR_VGA
+-  DRM_MODE_CONNECTOR_DVII
+-  DRM_MODE_CONNECTOR_DVID
+-  DRM_MODE_CONNECTOR_DVIA
+-  DRM_MODE_CONNECTOR_Composite
+-  DRM_MODE_CONNECTOR_SVIDEO
+-  DRM_MODE_CONNECTOR_LVDS
+-  DRM_MODE_CONNECTOR_Component
+-  DRM_MODE_CONNECTOR_9PinDIN
+-  DRM_MODE_CONNECTOR_DisplayPort
+-  DRM_MODE_CONNECTOR_HDMIA
+-  DRM_MODE_CONNECTOR_HDMIB
+-  DRM_MODE_CONNECTOR_TV
+-  DRM_MODE_CONNECTOR_eDP
+-  DRM_MODE_CONNECTOR_VIRTUAL
+
+Connectors must be attached to an encoder to be used. For devices that
+map connectors to encoders 1:1, the connector should be attached at
+initialization time with a call to
+:c:func:`drm_mode_connector_attach_encoder()`. The driver must
+also set the :c:type:`struct drm_connector <drm_connector>`
+encoder field to point to the attached encoder.
+
+Finally, drivers must initialize the connectors state change detection
+with a call to :c:func:`drm_kms_helper_poll_init()`. If at least
+one connector is pollable but can't generate hotplug interrupts
+(indicated by the DRM_CONNECTOR_POLL_CONNECT and
+DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
+automatically be queued to periodically poll for changes. Connectors
+that can generate hotplug interrupts must be marked with the
+DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
+call :c:func:`drm_helper_hpd_irq_event()`. The function will
+queue a delayed work to check the state of all connectors, but no
+periodic polling will be done.
+
+Connector Operations
+~~~~~~~~~~~~~~~~~~~~
+
+    **Note**
+
+    Unless otherwise state, all operations are mandatory.
+
+DPMS
+''''
+
+void (\*dpms)(struct drm_connector \*connector, int mode);
+The DPMS operation sets the power state of a connector. The mode
+argument is one of
+
+-  DRM_MODE_DPMS_ON
+
+-  DRM_MODE_DPMS_STANDBY
+
+-  DRM_MODE_DPMS_SUSPEND
+
+-  DRM_MODE_DPMS_OFF
+
+In all but DPMS_ON mode the encoder to which the connector is attached
+should put the display in low-power mode by driving its signals
+appropriately. If more than one connector is attached to the encoder
+care should be taken not to change the power state of other displays as
+a side effect. Low-power mode should be propagated to the encoders and
+CRTCs when all related connectors are put in low-power mode.
+
+Modes
+'''''
+
+int (\*fill_modes)(struct drm_connector \*connector, uint32_t
+max_width, uint32_t max_height);
+Fill the mode list with all supported modes for the connector. If the
+``max_width`` and ``max_height`` arguments are non-zero, the
+implementation must ignore all modes wider than ``max_width`` or higher
+than ``max_height``.
+
+The connector must also fill in this operation its display_info
+width_mm and height_mm fields with the connected display physical size
+in millimeters. The fields should be set to 0 if the value isn't known
+or is not applicable (for instance for projector devices).
+
+Connection Status
+'''''''''''''''''
+
+The connection status is updated through polling or hotplug events when
+supported (see ?). The status value is reported to userspace through
+ioctls and must not be used inside the driver, as it only gets
+initialized by a call to :c:func:`drm_mode_getconnector()` from
+userspace.
+
+enum drm_connector_status (\*detect)(struct drm_connector
+\*connector, bool force);
+Check to see if anything is attached to the connector. The ``force``
+parameter is set to false whilst polling or to true when checking the
+connector due to user request. ``force`` can be used by the driver to
+avoid expensive, destructive operations during automated probing.
+
+Return connector_status_connected if something is connected to the
+connector, connector_status_disconnected if nothing is connected and
+connector_status_unknown if the connection state isn't known.
+
+Drivers should only return connector_status_connected if the
+connection status has really been probed as connected. Connectors that
+can't detect the connection status, or failed connection status probes,
+should return connector_status_unknown.
+
+Cleanup
+-------
+
+The DRM core manages its objects' lifetime. When an object is not needed
+anymore the core calls its destroy function, which must clean up and
+free every resource allocated for the object. Every
+:c:func:`drm_\*_init()` call must be matched with a corresponding
+:c:func:`drm_\*_cleanup()` call to cleanup CRTCs
+(:c:func:`drm_crtc_cleanup()`), planes
+(:c:func:`drm_plane_cleanup()`), encoders
+(:c:func:`drm_encoder_cleanup()`) and connectors
+(:c:func:`drm_connector_cleanup()`). Furthermore, connectors that
+have been added to sysfs must be removed by a call to
+:c:func:`drm_connector_unregister()` before calling
+:c:func:`drm_connector_cleanup()`.
+
+Connectors state change detection must be cleanup up with a call to
+:c:func:`drm_kms_helper_poll_fini()`.
+
+Output discovery and initialization example
+-------------------------------------------
+
+::
+
+    void intel_crt_init(struct drm_device *dev)
+    {
+        struct drm_connector *connector;
+        struct intel_output *intel_output;
+
+        intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
+        if (!intel_output)
+            return;
+
+        connector = &intel_output->base;
+        drm_connector_init(dev, &intel_output->base,
+                   &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
+
+        drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
+                 DRM_MODE_ENCODER_DAC);
+
+        drm_mode_connector_attach_encoder(&intel_output->base,
+                          &intel_output->enc);
+
+        /* Set up the DDC bus. */
+        intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
+        if (!intel_output->ddc_bus) {
+            dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
+                   "failed.\n");
+            return;
+        }
+
+        intel_output->type = INTEL_OUTPUT_ANALOG;
+        connector->interlace_allowed = 0;
+        connector->doublescan_allowed = 0;
+
+        drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
+        drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
+
+        drm_connector_register(connector);
+    }
+
+In the example above (taken from the i915 driver), a CRTC, connector and
+encoder combination is created. A device-specific i2c bus is also
+created for fetching EDID data and performing monitor detection. Once
+the process is complete, the new connector is registered with sysfs to
+make its properties available to applications.
+
+KMS API Functions
+-----------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
+   :export:
+
+KMS Data Structures
+-------------------
+
+.. kernel-doc:: include/drm/drm_crtc.h
+   :internal:
+
+KMS Locking
+-----------
+
+.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
+   :doc: kms locking
+
+.. kernel-doc:: include/drm/drm_modeset_lock.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
+   :export:
+
+KMS Properties
+==============
+
+Drivers may need to expose additional parameters to applications than
+those described in the previous sections. KMS supports attaching
+properties to CRTCs, connectors and planes and offers a userspace API to
+list, get and set the property values.
+
+Properties are identified by a name that uniquely defines the property
+purpose, and store an associated value. For all property types except
+blob properties the value is a 64-bit unsigned integer.
+
+KMS differentiates between properties and property instances. Drivers
+first create properties and then create and associate individual
+instances of those properties to objects. A property can be instantiated
+multiple times and associated with different objects. Values are stored
+in property instances, and all other property information are stored in
+the property and shared between all instances of the property.
+
+Every property is created with a type that influences how the KMS core
+handles the property. Supported property types are
+
+DRM_MODE_PROP_RANGE
+    Range properties report their minimum and maximum admissible values.
+    The KMS core verifies that values set by application fit in that
+    range.
+
+DRM_MODE_PROP_ENUM
+    Enumerated properties take a numerical value that ranges from 0 to
+    the number of enumerated values defined by the property minus one,
+    and associate a free-formed string name to each value. Applications
+    can retrieve the list of defined value-name pairs and use the
+    numerical value to get and set property instance values.
+
+DRM_MODE_PROP_BITMASK
+    Bitmask properties are enumeration properties that additionally
+    restrict all enumerated values to the 0..63 range. Bitmask property
+    instance values combine one or more of the enumerated bits defined
+    by the property.
+
+DRM_MODE_PROP_BLOB
+    Blob properties store a binary blob without any format restriction.
+    The binary blobs are created as KMS standalone objects, and blob
+    property instance values store the ID of their associated blob
+    object.
+
+    Blob properties are only used for the connector EDID property and
+    cannot be created by drivers.
+
+To create a property drivers call one of the following functions
+depending on the property type. All property creation functions take
+property flags and name, as well as type-specific arguments.
+
+-  struct drm_property \*drm_property_create_range(struct
+   drm_device \*dev, int flags, const char \*name, uint64_t min,
+   uint64_t max);
+   Create a range property with the given minimum and maximum values.
+
+-  struct drm_property \*drm_property_create_enum(struct drm_device
+   \*dev, int flags, const char \*name, const struct
+   drm_prop_enum_list \*props, int num_values);
+   Create an enumerated property. The ``props`` argument points to an
+   array of ``num_values`` value-name pairs.
+
+-  struct drm_property \*drm_property_create_bitmask(struct
+   drm_device \*dev, int flags, const char \*name, const struct
+   drm_prop_enum_list \*props, int num_values);
+   Create a bitmask property. The ``props`` argument points to an array
+   of ``num_values`` value-name pairs.
+
+Properties can additionally be created as immutable, in which case they
+will be read-only for applications but can be modified by the driver. To
+create an immutable property drivers must set the
+DRM_MODE_PROP_IMMUTABLE flag at property creation time.
+
+When no array of value-name pairs is readily available at property
+creation time for enumerated or range properties, drivers can create the
+property using the :c:func:`drm_property_create()` function and
+manually add enumeration value-name pairs by calling the
+:c:func:`drm_property_add_enum()` function. Care must be taken to
+properly specify the property type through the ``flags`` argument.
+
+After creating properties drivers can attach property instances to CRTC,
+connector and plane objects by calling the
+:c:func:`drm_object_attach_property()`. The function takes a
+pointer to the target object, a pointer to the previously created
+property and an initial instance value.
+
+Existing KMS Properties
+-----------------------
+
+The following table gives description of drm properties exposed by
+various modules/drivers.
+
+.. csv-table::
+   :header-rows: 1
+   :file: kms-properties.csv
+
+Vertical Blanking
+=================
+
+Vertical blanking plays a major role in graphics rendering. To achieve
+tear-free display, users must synchronize page flips and/or rendering to
+vertical blanking. The DRM API offers ioctls to perform page flips
+synchronized to vertical blanking and wait for vertical blanking.
+
+The DRM core handles most of the vertical blanking management logic,
+which involves filtering out spurious interrupts, keeping race-free
+blanking counters, coping with counter wrap-around and resets and
+keeping use counts. It relies on the driver to generate vertical
+blanking interrupts and optionally provide a hardware vertical blanking
+counter. Drivers must implement the following operations.
+
+-  int (\*enable_vblank) (struct drm_device \*dev, int crtc); void
+   (\*disable_vblank) (struct drm_device \*dev, int crtc);
+   Enable or disable vertical blanking interrupts for the given CRTC.
+
+-  u32 (\*get_vblank_counter) (struct drm_device \*dev, int crtc);
+   Retrieve the value of the vertical blanking counter for the given
+   CRTC. If the hardware maintains a vertical blanking counter its value
+   should be returned. Otherwise drivers can use the
+   :c:func:`drm_vblank_count()` helper function to handle this
+   operation.
+
+Drivers must initialize the vertical blanking handling core with a call
+to :c:func:`drm_vblank_init()` in their load operation.
+
+Vertical blanking interrupts can be enabled by the DRM core or by
+drivers themselves (for instance to handle page flipping operations).
+The DRM core maintains a vertical blanking use count to ensure that the
+interrupts are not disabled while a user still needs them. To increment
+the use count, drivers call :c:func:`drm_vblank_get()`. Upon
+return vertical blanking interrupts are guaranteed to be enabled.
+
+To decrement the use count drivers call
+:c:func:`drm_vblank_put()`. Only when the use count drops to zero
+will the DRM core disable the vertical blanking interrupts after a delay
+by scheduling a timer. The delay is accessible through the
+vblankoffdelay module parameter or the ``drm_vblank_offdelay`` global
+variable and expressed in milliseconds. Its default value is 5000 ms.
+Zero means never disable, and a negative value means disable
+immediately. Drivers may override the behaviour by setting the
+:c:type:`struct drm_device <drm_device>`
+vblank_disable_immediate flag, which when set causes vblank interrupts
+to be disabled immediately regardless of the drm_vblank_offdelay
+value. The flag should only be set if there's a properly working
+hardware vblank counter present.
+
+When a vertical blanking interrupt occurs drivers only need to call the
+:c:func:`drm_handle_vblank()` function to account for the
+interrupt.
+
+Resources allocated by :c:func:`drm_vblank_init()` must be freed
+with a call to :c:func:`drm_vblank_cleanup()` in the driver unload
+operation handler.
+
+Vertical Blanking and Interrupt Handling Functions Reference
+------------------------------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_irq.c
+   :export:
+
+.. kernel-doc:: include/drm/drmP.h
+   :functions: drm_crtc_vblank_waitqueue

Documentation/gpu/drm-mm.rst

+=====================
+DRM Memory Management
+=====================
+
+Modern Linux systems require large amount of graphics memory to store
+frame buffers, textures, vertices and other graphics-related data. Given
+the very dynamic nature of many of that data, managing graphics memory
+efficiently is thus crucial for the graphics stack and plays a central
+role in the DRM infrastructure.
+
+The DRM core includes two memory managers, namely Translation Table Maps
+(TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
+manager to be developed and tried to be a one-size-fits-them all
+solution. It provides a single userspace API to accommodate the need of
+all hardware, supporting both Unified Memory Architecture (UMA) devices
+and devices with dedicated video RAM (i.e. most discrete video cards).
+This resulted in a large, complex piece of code that turned out to be
+hard to use for driver development.
+
+GEM started as an Intel-sponsored project in reaction to TTM's
+complexity. Its design philosophy is completely different: instead of
+providing a solution to every graphics memory-related problems, GEM
+identified common code between drivers and created a support library to
+share it. GEM has simpler initialization and execution requirements than
+TTM, but has no video RAM management capabilities and is thus limited to
+UMA devices.
+
+The Translation Table Manager (TTM)
+-----------------------------------
+
+TTM design background and information belongs here.
+
+TTM initialization
+~~~~~~~~~~~~~~~~~~
+
+    **Warning**
+
+    This section is outdated.
+
+Drivers wishing to support TTM must fill out a drm_bo_driver
+structure. The structure contains several fields with function pointers
+for initializing the TTM, allocating and freeing memory, waiting for
+command completion and fence synchronization, and memory migration. See
+the radeon_ttm.c file for an example of usage.
+
+The ttm_global_reference structure is made up of several fields:
+
+::
+
+              struct ttm_global_reference {
+                      enum ttm_global_types global_type;
+                      size_t size;
+                      void *object;
+                      int (*init) (struct ttm_global_reference *);
+                      void (*release) (struct ttm_global_reference *);
+              };
+
+
+There should be one global reference structure for your memory manager
+as a whole, and there will be others for each object created by the
+memory manager at runtime. Your global TTM should have a type of
+TTM_GLOBAL_TTM_MEM. The size field for the global object should be
+sizeof(struct ttm_mem_global), and the init and release hooks should
+point at your driver-specific init and release routines, which probably
+eventually call ttm_mem_global_init and ttm_mem_global_release,
+respectively.
+
+Once your global TTM accounting structure is set up and initialized by
+calling ttm_global_item_ref() on it, you need to create a buffer
+object TTM to provide a pool for buffer object allocation by clients and
+the kernel itself. The type of this object should be
+TTM_GLOBAL_TTM_BO, and its size should be sizeof(struct
+ttm_bo_global). Again, driver-specific init and release functions may
+be provided, likely eventually calling ttm_bo_global_init() and
+ttm_bo_global_release(), respectively. Also, like the previous
+object, ttm_global_item_ref() is used to create an initial reference
+count for the TTM, which will call your initialization function.
+
+The Graphics Execution Manager (GEM)
+------------------------------------
+
+The GEM design approach has resulted in a memory manager that doesn't
+provide full coverage of all (or even all common) use cases in its
+userspace or kernel API. GEM exposes a set of standard memory-related
+operations to userspace and a set of helper functions to drivers, and
+let drivers implement hardware-specific operations with their own
+private API.
+
+The GEM userspace API is described in the `GEM - the Graphics Execution
+Manager <http://lwn.net/Articles/283798/>`__ article on LWN. While
+slightly outdated, the document provides a good overview of the GEM API
+principles. Buffer allocation and read and write operations, described
+as part of the common GEM API, are currently implemented using
+driver-specific ioctls.
+
+GEM is data-agnostic. It manages abstract buffer objects without knowing
+what individual buffers contain. APIs that require knowledge of buffer
+contents or purpose, such as buffer allocation or synchronization
+primitives, are thus outside of the scope of GEM and must be implemented
+using driver-specific ioctls.
+
+On a fundamental level, GEM involves several operations:
+
+-  Memory allocation and freeing
+-  Command execution
+-  Aperture management at command execution time
+
+Buffer object allocation is relatively straightforward and largely
+provided by Linux's shmem layer, which provides memory to back each
+object.
+
+Device-specific operations, such as command execution, pinning, buffer
+read & write, mapping, and domain ownership transfers are left to
+driver-specific ioctls.
+
+GEM Initialization
+~~~~~~~~~~~~~~~~~~
+
+Drivers that use GEM must set the DRIVER_GEM bit in the struct
+:c:type:`struct drm_driver <drm_driver>` driver_features
+field. The DRM core will then automatically initialize the GEM core
+before calling the load operation. Behind the scene, this will create a
+DRM Memory Manager object which provides an address space pool for
+object allocation.
+
+In a KMS configuration, drivers need to allocate and initialize a
+command ring buffer following core GEM initialization if required by the
+hardware. UMA devices usually have what is called a "stolen" memory
+region, which provides space for the initial framebuffer and large,
+contiguous memory regions required by the device. This space is
+typically not managed by GEM, and must be initialized separately into
+its own DRM MM object.
+
+GEM Objects Creation
+~~~~~~~~~~~~~~~~~~~~
+
+GEM splits creation of GEM objects and allocation of the memory that
+backs them in two distinct operations.
+
+GEM objects are represented by an instance of struct :c:type:`struct
+drm_gem_object <drm_gem_object>`. Drivers usually need to
+extend GEM objects with private information and thus create a
+driver-specific GEM object structure type that embeds an instance of
+struct :c:type:`struct drm_gem_object <drm_gem_object>`.
+
+To create a GEM object, a driver allocates memory for an instance of its
+specific GEM object type and initializes the embedded struct
+:c:type:`struct drm_gem_object <drm_gem_object>` with a call
+to :c:func:`drm_gem_object_init()`. The function takes a pointer
+to the DRM device, a pointer to the GEM object and the buffer object
+size in bytes.
+
+GEM uses shmem to allocate anonymous pageable memory.
+:c:func:`drm_gem_object_init()` will create an shmfs file of the
+requested size and store it into the struct :c:type:`struct
+drm_gem_object <drm_gem_object>` filp field. The memory is
+used as either main storage for the object when the graphics hardware
+uses system memory directly or as a backing store otherwise.
+
+Drivers are responsible for the actual physical pages allocation by
+calling :c:func:`shmem_read_mapping_page_gfp()` for each page.
+Note that they can decide to allocate pages when initializing the GEM
+object, or to delay allocation until the memory is needed (for instance
+when a page fault occurs as a result of a userspace memory access or
+when the driver needs to start a DMA transfer involving the memory).
+
+Anonymous pageable memory allocation is not always desired, for instance
+when the hardware requires physically contiguous system memory as is
+often the case in embedded devices. Drivers can create GEM objects with
+no shmfs backing (called private GEM objects) by initializing them with
+a call to :c:func:`drm_gem_private_object_init()` instead of
+:c:func:`drm_gem_object_init()`. Storage for private GEM objects
+must be managed by drivers.
+
+GEM Objects Lifetime
+~~~~~~~~~~~~~~~~~~~~
+
+All GEM objects are reference-counted by the GEM core. References can be
+acquired and release by :c:func:`calling
+drm_gem_object_reference()` and
+:c:func:`drm_gem_object_unreference()` respectively. The caller
+must hold the :c:type:`struct drm_device <drm_device>`
+struct_mutex lock when calling
+:c:func:`drm_gem_object_reference()`. As a convenience, GEM
+provides :c:func:`drm_gem_object_unreference_unlocked()`
+functions that can be called without holding the lock.
+
+When the last reference to a GEM object is released the GEM core calls
+the :c:type:`struct drm_driver <drm_driver>` gem_free_object
+operation. That operation is mandatory for GEM-enabled drivers and must
+free the GEM object and all associated resources.
+
+void (\*gem_free_object) (struct drm_gem_object \*obj); Drivers are
+responsible for freeing all GEM object resources. This includes the
+resources created by the GEM core, which need to be released with
+:c:func:`drm_gem_object_release()`.
+
+GEM Objects Naming
+~~~~~~~~~~~~~~~~~~
+
+Communication between userspace and the kernel refers to GEM objects
+using local handles, global names or, more recently, file descriptors.
+All of those are 32-bit integer values; the usual Linux kernel limits
+apply to the file descriptors.
+
+GEM handles are local to a DRM file. Applications get a handle to a GEM
+object through a driver-specific ioctl, and can use that handle to refer
+to the GEM object in other standard or driver-specific ioctls. Closing a
+DRM file handle frees all its GEM handles and dereferences the
+associated GEM objects.
+
+To create a handle for a GEM object drivers call
+:c:func:`drm_gem_handle_create()`. The function takes a pointer
+to the DRM file and the GEM object and returns a locally unique handle.
+When the handle is no longer needed drivers delete it with a call to
+:c:func:`drm_gem_handle_delete()`. Finally the GEM object
+associated with a handle can be retrieved by a call to
+:c:func:`drm_gem_object_lookup()`.
+
+Handles don't take ownership of GEM objects, they only take a reference
+to the object that will be dropped when the handle is destroyed. To
+avoid leaking GEM objects, drivers must make sure they drop the
+reference(s) they own (such as the initial reference taken at object
+creation time) as appropriate, without any special consideration for the
+handle. For example, in the particular case of combined GEM object and
+handle creation in the implementation of the dumb_create operation,
+drivers must drop the initial reference to the GEM object before
+returning the handle.
+
+GEM names are similar in purpose to handles but are not local to DRM
+files. They can be passed between processes to reference a GEM object
+globally. Names can't be used directly to refer to objects in the DRM
+API, applications must convert handles to names and names to handles
+using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
+respectively. The conversion is handled by the DRM core without any
+driver-specific support.
+
+GEM also supports buffer sharing with dma-buf file descriptors through
+PRIME. GEM-based drivers must use the provided helpers functions to
+implement the exporting and importing correctly. See ?. Since sharing
+file descriptors is inherently more secure than the easily guessable and
+global GEM names it is the preferred buffer sharing mechanism. Sharing
+buffers through GEM names is only supported for legacy userspace.
+Furthermore PRIME also allows cross-device buffer sharing since it is
+based on dma-bufs.
+
+GEM Objects Mapping
+~~~~~~~~~~~~~~~~~~~
+
+Because mapping operations are fairly heavyweight GEM favours
+read/write-like access to buffers, implemented through driver-specific
+ioctls, over mapping buffers to userspace. However, when random access
+to the buffer is needed (to perform software rendering for instance),
+direct access to the object can be more efficient.
+
+The mmap system call can't be used directly to map GEM objects, as they
+don't have their own file handle. Two alternative methods currently
+co-exist to map GEM objects to userspace. The first method uses a
+driver-specific ioctl to perform the mapping operation, calling
+:c:func:`do_mmap()` under the hood. This is often considered
+dubious, seems to be discouraged for new GEM-enabled drivers, and will
+thus not be described here.
+
+The second method uses the mmap system call on the DRM file handle. void
+\*mmap(void \*addr, size_t length, int prot, int flags, int fd, off_t
+offset); DRM identifies the GEM object to be mapped by a fake offset
+passed through the mmap offset argument. Prior to being mapped, a GEM
+object must thus be associated with a fake offset. To do so, drivers
+must call :c:func:`drm_gem_create_mmap_offset()` on the object.
+
+Once allocated, the fake offset value must be passed to the application
+in a driver-specific way and can then be used as the mmap offset
+argument.
+
+The GEM core provides a helper method :c:func:`drm_gem_mmap()` to
+handle object mapping. The method can be set directly as the mmap file
+operation handler. It will look up the GEM object based on the offset
+value and set the VMA operations to the :c:type:`struct drm_driver
+<drm_driver>` gem_vm_ops field. Note that
+:c:func:`drm_gem_mmap()` doesn't map memory to userspace, but
+relies on the driver-provided fault handler to map pages individually.
+
+To use :c:func:`drm_gem_mmap()`, drivers must fill the struct
+:c:type:`struct drm_driver <drm_driver>` gem_vm_ops field
+with a pointer to VM operations.
+
+struct vm_operations_struct \*gem_vm_ops struct
+vm_operations_struct { void (\*open)(struct vm_area_struct \* area);
+void (\*close)(struct vm_area_struct \* area); int (\*fault)(struct
+vm_area_struct \*vma, struct vm_fault \*vmf); };
+
+The open and close operations must update the GEM object reference
+count. Drivers can use the :c:func:`drm_gem_vm_open()` and
+:c:func:`drm_gem_vm_close()` helper functions directly as open
+and close handlers.
+
+The fault operation handler is responsible for mapping individual pages
+to userspace when a page fault occurs. Depending on the memory
+allocation scheme, drivers can allocate pages at fault time, or can
+decide to allocate memory for the GEM object at the time the object is
+created.
+
+Drivers that want to map the GEM object upfront instead of handling page
+faults can implement their own mmap file operation handler.
+
+Memory Coherency
+~~~~~~~~~~~~~~~~
+
+When mapped to the device or used in a command buffer, backing pages for
+an object are flushed to memory and marked write combined so as to be
+coherent with the GPU. Likewise, if the CPU accesses an object after the
+GPU has finished rendering to the object, then the object must be made
+coherent with the CPU's view of memory, usually involving GPU cache
+flushing of various kinds. This core CPU<->GPU coherency management is
+provided by a device-specific ioctl, which evaluates an object's current
+domain and performs any necessary flushing or synchronization to put the
+object into the desired coherency domain (note that the object may be
+busy, i.e. an active render target; in that case, setting the domain
+blocks the client and waits for rendering to complete before performing
+any necessary flushing operations).
+
+Command Execution
+~~~~~~~~~~~~~~~~~
+
+Perhaps the most important GEM function for GPU devices is providing a
+command execution interface to clients. Client programs construct
+command buffers containing references to previously allocated memory
+objects, and then submit them to GEM. At that point, GEM takes care to
+bind all the objects into the GTT, execute the buffer, and provide
+necessary synchronization between clients accessing the same buffers.
+This often involves evicting some objects from the GTT and re-binding
+others (a fairly expensive operation), and providing relocation support
+which hides fixed GTT offsets from clients. Clients must take care not
+to submit command buffers that reference more objects than can fit in
+the GTT; otherwise, GEM will reject them and no rendering will occur.
+Similarly, if several objects in the buffer require fence registers to
+be allocated for correct rendering (e.g. 2D blits on pre-965 chips),
+care must be taken not to require more fence registers than are
+available to the client. Such resource management should be abstracted
+from the client in libdrm.
+
+GEM Function Reference
+----------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_gem.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_gem.h
+   :internal:
+
+VMA Offset Manager
+------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c
+   :doc: vma offset manager
+
+.. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_vma_manager.h
+   :internal:
+
+PRIME Buffer Sharing
+--------------------
+
+PRIME is the cross device buffer sharing framework in drm, originally
+created for the OPTIMUS range of multi-gpu platforms. To userspace PRIME
+buffers are dma-buf based file descriptors.
+
+Overview and Driver Interface
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Similar to GEM global names, PRIME file descriptors are also used to
+share buffer objects across processes. They offer additional security:
+as file descriptors must be explicitly sent over UNIX domain sockets to
+be shared between applications, they can't be guessed like the globally
+unique GEM names.
+
+Drivers that support the PRIME API must set the DRIVER_PRIME bit in the
+struct :c:type:`struct drm_driver <drm_driver>`
+driver_features field, and implement the prime_handle_to_fd and
+prime_fd_to_handle operations.
+
+int (\*prime_handle_to_fd)(struct drm_device \*dev, struct drm_file
+\*file_priv, uint32_t handle, uint32_t flags, int \*prime_fd); int
+(\*prime_fd_to_handle)(struct drm_device \*dev, struct drm_file
+\*file_priv, int prime_fd, uint32_t \*handle); Those two operations
+convert a handle to a PRIME file descriptor and vice versa. Drivers must
+use the kernel dma-buf buffer sharing framework to manage the PRIME file
+descriptors. Similar to the mode setting API PRIME is agnostic to the
+underlying buffer object manager, as long as handles are 32bit unsigned
+integers.
+
+While non-GEM drivers must implement the operations themselves, GEM
+drivers must use the :c:func:`drm_gem_prime_handle_to_fd()` and
+:c:func:`drm_gem_prime_fd_to_handle()` helper functions. Those
+helpers rely on the driver gem_prime_export and gem_prime_import
+operations to create a dma-buf instance from a GEM object (dma-buf
+exporter role) and to create a GEM object from a dma-buf instance
+(dma-buf importer role).
+
+struct dma_buf \* (\*gem_prime_export)(struct drm_device \*dev,
+struct drm_gem_object \*obj, int flags); struct drm_gem_object \*
+(\*gem_prime_import)(struct drm_device \*dev, struct dma_buf
+\*dma_buf); These two operations are mandatory for GEM drivers that
+support PRIME.
+
+PRIME Helper Functions
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/drm_prime.c
+   :doc: PRIME Helpers
+
+PRIME Function References
+-------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_prime.c
+   :export:
+
+DRM MM Range Allocator
+----------------------
+
+Overview
+~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/drm_mm.c
+   :doc: Overview
+
+LRU Scan/Eviction Support
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/drm_mm.c
+   :doc: lru scan roaster
+
+DRM MM Range Allocator Function References
+------------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_mm.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_mm.h
+   :internal:
+
+CMA Helper Functions Reference
+------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
+   :doc: cma helpers
+
+.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_gem_cma_helper.h
+   :internal:

Documentation/gpu/index.rst

@@ -6,6 +6,9 @@ Linux GPU Driver Developer's Guide
 
    introduction
    drm-internals
+   drm-mm
+   drm-kms
+   drm-kms-helpers
    drm-uapi
    i915
    vga-switcheroo