drm: Allow drivers to indicate the damage helpers to ignore damage clips

It allows drivers to set a struct drm_plane_state .ignore_damage_clips in
their plane's .atomic_check callback, as an indication to damage helpers
such as drm_atomic_helper_damage_iter_init() that the damage clips should
be ignored.

To be used by drivers that do per-buffer (e.g: virtio-gpu) uploads (rather
than per-plane uploads), since these type of drivers need to handle buffer
damages instead of frame damages.

That way, these drivers could force a full plane update if the framebuffer
attached to a plane's state has changed since the last update (page-flip).

Fixes: 01f05940a9a7 ("drm/virtio: Enable fb damage clips property for the primary plane")
Cc: <[e-mail]> # v6.4+
Reported-by: nerdopolis <[e-mail]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218115
Suggested-by: Thomas Zimmermann <[e-mail]>
Signed-off-by: Javier Martinez Canillas <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Zack Rusin <[e-mail]>
Acked-by: Sima Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/gpu/drm-kms.rst

···
 .. kernel-doc:: drivers/gpu/drm/drm_blend.c
    :doc: overview
 
+.. _damage_tracking_properties:
+
 Damage Tracking Properties
 --------------------------
 

drivers/gpu/drm/drm_damage_helper.c

···
 	iter->plane_src.x2 = (src.x2 >> 16) + !!(src.x2 & 0xFFFF);
 	iter->plane_src.y2 = (src.y2 >> 16) + !!(src.y2 & 0xFFFF);
 
-	if (!iter->clips || !drm_rect_equals(&state->src, &old_state->src)) {
+	if (!iter->clips || state->ignore_damage_clips ||
+	    !drm_rect_equals(&state->src, &old_state->src)) {
 		iter->clips = NULL;
 		iter->num_clips = 0;
 		iter->full_update = true;

include/drm/drm_plane.h

···
 	struct drm_property_blob *fb_damage_clips;
 
 	/**
+	 * @ignore_damage_clips:
+	 *
+	 * Set by drivers to indicate the drm_atomic_helper_damage_iter_init()
+	 * helper that the @fb_damage_clips blob property should be ignored.
+	 *
+	 * See :ref:`damage_tracking_properties` for more information.
+	 */
+	bool ignore_damage_clips;
+
+	/**
 	 * @src:
 	 *
 	 * source coordinates of the plane (in 16.16).