Documentation: PCI: Guide to use PCI Endpoint Core Layer

Add Documentation to help users use endpoint library to enable endpoint
mode in the PCI controller and add new PCI endpoint functions.
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-By: Joao Pinto <jpinto@synopsys.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Documentation/PCI/00-INDEX

@@ -12,3 +12,5 @@ pci.txt
 	- info on the PCI subsystem for device driver authors
 pcieaer-howto.txt
 	- the PCI Express Advanced Error Reporting Driver Guide HOWTO
+endpoint/pci-endpoint.txt
+	- guide to add endpoint controller driver and endpoint function driver.

Documentation/PCI/endpoint/pci-endpoint.txt

+			    PCI ENDPOINT FRAMEWORK
+		    Kishon Vijay Abraham I <kishon@ti.com>
+
+This document is a guide to use the PCI Endpoint Framework in order to create
+endpoint controller driver, endpoint function driver, and using configfs
+interface to bind the function driver to the controller driver.
+
+1. Introduction
+
+Linux has a comprehensive PCI subsystem to support PCI controllers that
+operates in Root Complex mode. The subsystem has capability to scan PCI bus,
+assign memory resources and IRQ resources, load PCI driver (based on
+vendor ID, device ID), support other services like hot-plug, power management,
+advanced error reporting and virtual channels.
+
+However the PCI controller IP integrated in some SoCs is capable of operating
+either in Root Complex mode or Endpoint mode. PCI Endpoint Framework will
+add endpoint mode support in Linux. This will help to run Linux in an
+EP system which can have a wide variety of use cases from testing or
+validation, co-processor accelerator, etc.
+
+2. PCI Endpoint Core
+
+The PCI Endpoint Core layer comprises 3 components: the Endpoint Controller
+library, the Endpoint Function library, and the configfs layer to bind the
+endpoint function with the endpoint controller.
+
+2.1 PCI Endpoint Controller(EPC) Library
+
+The EPC library provides APIs to be used by the controller that can operate
+in endpoint mode. It also provides APIs to be used by function driver/library
+in order to implement a particular endpoint function.
+
+2.1.1 APIs for the PCI controller Driver
+
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI controller driver.
+
+*) devm_pci_epc_create()/pci_epc_create()
+
+   The PCI controller driver should implement the following ops:
+	 * write_header: ops to populate configuration space header
+	 * set_bar: ops to configure the BAR
+	 * clear_bar: ops to reset the BAR
+	 * alloc_addr_space: ops to allocate in PCI controller address space
+	 * free_addr_space: ops to free the allocated address space
+	 * raise_irq: ops to raise a legacy or MSI interrupt
+	 * start: ops to start the PCI link
+	 * stop: ops to stop the PCI link
+
+   The PCI controller driver can then create a new EPC device by invoking
+   devm_pci_epc_create()/pci_epc_create().
+
+*) devm_pci_epc_destroy()/pci_epc_destroy()
+
+   The PCI controller driver can destroy the EPC device created by either
+   devm_pci_epc_create() or pci_epc_create() using devm_pci_epc_destroy() or
+   pci_epc_destroy().
+
+*) pci_epc_linkup()
+
+   In order to notify all the function devices that the EPC device to which
+   they are linked has established a link with the host, the PCI controller
+   driver should invoke pci_epc_linkup().
+
+*) pci_epc_mem_init()
+
+   Initialize the pci_epc_mem structure used for allocating EPC addr space.
+
+*) pci_epc_mem_exit()
+
+   Cleanup the pci_epc_mem structure allocated during pci_epc_mem_init().
+
+2.1.2 APIs for the PCI Endpoint Function Driver
+
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI endpoint function driver.
+
+*) pci_epc_write_header()
+
+   The PCI endpoint function driver should use pci_epc_write_header() to
+   write the standard configuration header to the endpoint controller.
+
+*) pci_epc_set_bar()
+
+   The PCI endpoint function driver should use pci_epc_set_bar() to configure
+   the Base Address Register in order for the host to assign PCI addr space.
+   Register space of the function driver is usually configured
+   using this API.
+
+*) pci_epc_clear_bar()
+
+   The PCI endpoint function driver should use pci_epc_clear_bar() to reset
+   the BAR.
+
+*) pci_epc_raise_irq()
+
+   The PCI endpoint function driver should use pci_epc_raise_irq() to raise
+   Legacy Interrupt or MSI Interrupt.
+
+*) pci_epc_mem_alloc_addr()
+
+   The PCI endpoint function driver should use pci_epc_mem_alloc_addr(), to
+   allocate memory address from EPC addr space which is required to access
+   RC's buffer
+
+*) pci_epc_mem_free_addr()
+
+   The PCI endpoint function driver should use pci_epc_mem_free_addr() to
+   free the memory space allocated using pci_epc_mem_alloc_addr().
+
+2.1.3 Other APIs
+
+There are other APIs provided by the EPC library. These are used for binding
+the EPF device with EPC device. pci-ep-cfs.c can be used as reference for
+using these APIs.
+
+*) pci_epc_get()
+
+   Get a reference to the PCI endpoint controller based on the device name of
+   the controller.
+
+*) pci_epc_put()
+
+   Release the reference to the PCI endpoint controller obtained using
+   pci_epc_get()
+
+*) pci_epc_add_epf()
+
+   Add a PCI endpoint function to a PCI endpoint controller. A PCIe device
+   can have up to 8 functions according to the specification.
+
+*) pci_epc_remove_epf()
+
+   Remove the PCI endpoint function from PCI endpoint controller.
+
+*) pci_epc_start()
+
+   The PCI endpoint function driver should invoke pci_epc_start() once it
+   has configured the endpoint function and wants to start the PCI link.
+
+*) pci_epc_stop()
+
+   The PCI endpoint function driver should invoke pci_epc_stop() to stop
+   the PCI LINK.
+
+2.2 PCI Endpoint Function(EPF) Library
+
+The EPF library provides APIs to be used by the function driver and the EPC
+library to provide endpoint mode functionality.
+
+2.2.1 APIs for the PCI Endpoint Function Driver
+
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI endpoint function driver.
+
+*) pci_epf_register_driver()
+
+   The PCI Endpoint Function driver should implement the following ops:
+	 * bind: ops to perform when a EPC device has been bound to EPF device
+	 * unbind: ops to perform when a binding has been lost between a EPC
+	   device and EPF device
+	 * linkup: ops to perform when the EPC device has established a
+	   connection with a host system
+
+  The PCI Function driver can then register the PCI EPF driver by using
+  pci_epf_register_driver().
+
+*) pci_epf_unregister_driver()
+
+  The PCI Function driver can unregister the PCI EPF driver by using
+  pci_epf_unregister_driver().
+
+*) pci_epf_alloc_space()
+
+  The PCI Function driver can allocate space for a particular BAR using
+  pci_epf_alloc_space().
+
+*) pci_epf_free_space()
+
+  The PCI Function driver can free the allocated space
+  (using pci_epf_alloc_space) by invoking pci_epf_free_space().
+
+2.2.2 APIs for the PCI Endpoint Controller Library
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI endpoint controller library.
+
+*) pci_epf_linkup()
+
+   The PCI endpoint controller library invokes pci_epf_linkup() when the
+   EPC device has established the connection to the host.
+
+2.2.2 Other APIs
+There are other APIs provided by the EPF library. These are used to notify
+the function driver when the EPF device is bound to the EPC device.
+pci-ep-cfs.c can be used as reference for using these APIs.
+
+*) pci_epf_create()
+
+   Create a new PCI EPF device by passing the name of the PCI EPF device.
+   This name will be used to bind the the EPF device to a EPF driver.
+
+*) pci_epf_destroy()
+
+   Destroy the created PCI EPF device.
+
+*) pci_epf_bind()
+
+   pci_epf_bind() should be invoked when the EPF device has been bound to
+   a EPC device.
+
+*) pci_epf_unbind()
+
+   pci_epf_unbind() should be invoked when the binding between EPC device
+   and EPF device is lost.