drm/atomic-helper: Don't allocate new plane state in CRTC check

[ Upstream commit dbbf933 ]

In drm_atomic_helper_check_crtc_state(), do not add a new plane state
to the global state if it does not exist already. Adding a new plane
state will result in overhead for the plane during the atomic-commit
step.

For the test in drm_atomic_helper_check_crtc_state() to succeed, it
is important that the CRTC has an enabled primary plane after the
commit. Simply testing the CRTC state's plane_mask for a primary plane
is sufficient.

Note that the helper still only tests for an attached primary plane.
Drivers have to ensure that the plane contains valid pixel information.

v5:
	* fix commit description (Javier)
v3:
	* test for a primary plane in plane_mask (Ville)
v2:
	* remove unnecessary test for plane->crtc (Ville)
	* inline drm_atomic_get_next_plane_state() (Ville)
	* acquire plane lock before accessing plane->state (Ville)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Fixes: d6b9af1 ("drm/atomic-helper: Add helper drm_atomic_helper_check_crtc_state()")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20221007124338.24152-2-tzimmermann@suse.de
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/gpu/drm/drm_atomic_helper.c

@@ -945,7 +945,6 @@ int drm_atomic_helper_check_crtc_state(struct drm_crtc_state *crtc_state,
 				       bool can_disable_primary_planes)
 {
 	struct drm_device *dev = crtc_state->crtc->dev;
-	struct drm_atomic_state *state = crtc_state->state;
 
 	if (!crtc_state->enable)
 		return 0;
@@ -956,14 +955,7 @@ int drm_atomic_helper_check_crtc_state(struct drm_crtc_state *crtc_state,
 		struct drm_plane *plane;
 
 		drm_for_each_plane_mask(plane, dev, crtc_state->plane_mask) {
-			struct drm_plane_state *plane_state;
-
-			if (plane->type != DRM_PLANE_TYPE_PRIMARY)
-				continue;
-			plane_state = drm_atomic_get_plane_state(state, plane);
-			if (IS_ERR(plane_state))
-				return PTR_ERR(plane_state);
-			if (plane_state->fb && plane_state->crtc) {
+			if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
 				has_primary_plane = true;
 				break;
 			}