drm: Update kerneldoc for drm_crtc.[hc]

After going through all the trouble of splitting out parts from
drm_crtc.[hc] and then properly documenting each I've entirely
forgotten to show the same TLC for CRTCs themselves!

Let's make amends asap.

v2: Review from Eric.
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Documentation/gpu/drm-kms.rst

@@ -48,11 +48,17 @@ CRTC Abstraction
 ================
 
 .. kernel-doc:: drivers/gpu/drm/drm_crtc.c
-   :export:
+   :doc: overview
+
+CRTC Functions Reference
+--------------------------------
 
 .. kernel-doc:: include/drm/drm_crtc.h
    :internal:
 
+.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
+   :export:
+
 Frame Buffer Abstraction
 ========================
 

drivers/gpu/drm/drm_crtc.c

@@ -46,6 +46,27 @@
 #include "drm_crtc_internal.h"
 #include "drm_internal.h"
 
+/**
+ * DOC: overview
+ *
+ * A CRTC represents the overall display pipeline. It receives pixel data from
+ * &drm_plane and blends them together. The &drm_display_mode is also attached
+ * to the CRTC, specifying display timings. On the output side the data is fed
+ * to one or more &drm_encoder, which are then each connected to one
+ * &drm_connector.
+ *
+ * To create a CRTC, a KMS drivers allocates and zeroes an instances of
+ * &struct drm_crtc (possibly as part of a larger structure) and registers it
+ * with a call to drm_crtc_init_with_planes().
+ *
+ * The CRTC is also the entry point for legacy modeset operations, see
+ * &drm_crtc_funcs.set_config, legacy plane operations, see
+ * &drm_crtc_funcs.page_flip and &drm_crtc_funcs.cursor_set2, and other legacy
+ * operations like &drm_crtc_funcs.gamma_set. For atomic drivers all these
+ * features are controlled through &drm_property and
+ * &drm_mode_config_funcs.atomic_check and &drm_mode_config_funcs.atomic_check.
+ */
+
 /**
  * drm_crtc_from_index - find the registered CRTC at an index
  * @dev: DRM device

include/drm/drm_crtc.h

@@ -641,7 +641,7 @@ struct drm_crtc {
 	 *
 	 * This provides a read lock for the overall crtc state (mode, dpms
 	 * state, ...) and a write lock for everything which can be update
-	 * without a full modeset (fb, cursor data, crtc properties ...). Full
+	 * without a full modeset (fb, cursor data, crtc properties ...). A full
 	 * modeset also need to grab &drm_mode_config.connection_mutex.
 	 */
 	struct drm_modeset_lock mutex;
@@ -774,10 +774,8 @@ struct drm_crtc {
  * @connectors: array of connectors to drive with this CRTC if possible
  * @num_connectors: size of @connectors array
  *
- * Represents a single crtc the connectors that it drives with what mode
- * and from which framebuffer it scans out from.
- *
- * This is used to set modes.
+ * This represents a modeset configuration for the legacy SETCRTC ioctl and is
+ * also used internally. Atomic drivers instead use &drm_atomic_state.
  */
 struct drm_mode_set {
 	struct drm_framebuffer *fb;
@@ -834,7 +832,15 @@ int drm_crtc_force_disable_all(struct drm_device *dev);
 int drm_mode_set_config_internal(struct drm_mode_set *set);
 struct drm_crtc *drm_crtc_from_index(struct drm_device *dev, int idx);
 
-/* Helpers */
+/**
+ * drm_crtc_find - look up a CRTC object from its ID
+ * @dev: DRM device
+ * @id: &drm_mode_object ID
+ *
+ * This can be used to look up a CRTC from its userspace ID. Only used by
+ * drivers for legacy IOCTLs and interface, nowadays extensions to the KMS
+ * userspace interface should be done using &drm_property.
+ */
 static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,
 	uint32_t id)
 {
@@ -843,6 +849,13 @@ static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,
 	return mo ? obj_to_crtc(mo) : NULL;
 }
 
+/**
+ * drm_for_each_crtc - iterate over all CRTCs
+ * @crtc: a &struct drm_crtc as the loop cursor
+ * @dev: the &struct drm_device
+ *
+ * Iterate over all CRTCs of @dev.
+ */
 #define drm_for_each_crtc(crtc, dev) \
 	list_for_each_entry(crtc, &(dev)->mode_config.crtc_list, head)