drm: writeback: document callbacks

Document the callbacks:
    drm_connector_helper_funcs.prepare_writeback_job
    drm_connector_helper_funcs.cleanup_writeback_job

The documentation was pulled from the changelong introducing the
callbacks, originally written by Laurent.

Adding the missing documentation fixes the following warnings:
drm_modeset_helper_vtables.h:1052: warning: Function parameter or member 'prepare_writeback_job' not described in 'drm_connector_helper_funcs'
drm_modeset_helper_vtables.h:1052: warning: Function parameter or member 'cleanup_writeback_job' not described in 'drm_connector_helper_funcs'

v2:
  - Fix formatting (Daniel)
  - Drop changelog text and add reference (Daniel)
  - Improve grammar. and use "operation" (Laurent)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Link: https://patchwork.freedesktop.org/patch/msgid/20200406194746.26433-3-sam@ravnborg.org

diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 7c20b1c..421a30f 100644 (file)
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -1075,8 +1075,35 @@ struct drm_connector_helper_funcs {
        void (*atomic_commit)(struct drm_connector *connector,
                              struct drm_connector_state *state);
 
+       /**
+        * @prepare_writeback_job:
+        *
+        * As writeback jobs contain a framebuffer, drivers may need to
+        * prepare and clean them up the same way they can prepare and
+        * clean up framebuffers for planes. This optional connector operation
+        * is used to support the preparation of writeback jobs. The job
+        * prepare operation is called from drm_atomic_helper_prepare_planes()
+        * for struct &drm_writeback_connector connectors only.
+        *
+        * This operation is optional.
+        *
+        * This callback is used by the atomic modeset helpers.
+        */
        int (*prepare_writeback_job)(struct drm_writeback_connector *connector,
                                     struct drm_writeback_job *job);
+       /**
+        * @cleanup_writeback_job:
+        *
+        * This optional connector operation is used to support the
+        * cleanup of writeback jobs. The job cleanup operation is called
+        * from the existing drm_writeback_cleanup_job() function, invoked
+        * both when destroying the job as part of an aborted commit, or when
+        * the job completes.
+        *
+        * This operation is optional.
+        *
+        * This callback is used by the atomic modeset helpers.
+        */
        void (*cleanup_writeback_job)(struct drm_writeback_connector *connector,
                                      struct drm_writeback_job *job);
 };