[PATCH] drm/atomic-helper: Don't allocated plane state in CRTC check

[Thomas Zimmermann <tzimmermann@suse.de>]

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 results 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.
This can be a newly enabled plane or an already enabled plane. So if a
plane is not part of the commit, use the plane's existing state. The new
helper drm_atomic_get_next_plane_state() returns the correct instance.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: d6b9af1097fe ("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
---
 drivers/gpu/drm/drm_atomic_helper.c |  4 +---
 include/drm/drm_atomic.h            | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 98cc3137c062..463d4f3fa443 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -960,9 +960,7 @@ int drm_atomic_helper_check_crtc_state(struct drm_crtc_state *crtc_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);
+			plane_state = drm_atomic_get_next_plane_state(state, plane);
 			if (plane_state->fb && plane_state->crtc) {
 				has_primary_plane = true;
 				break;
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 10b1990bc1f6..4006f2d459e3 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -623,6 +623,26 @@ drm_atomic_get_new_plane_state(struct drm_atomic_state *state,
 	return state->planes[drm_plane_index(plane)].new_state;
 }
 
+/**
+ * drm_atomic_get_next_plane_state - get plane state after atomic commit
+ * @state: global atomic state object
+ * @plane: plane to grab
+ *
+ * This function returns the plane state that the given plane will have
+ * after the atomic commit. This will be the new plane state if the plane
+ * is part of the global atomic state, or the current state otherwise.
+ */
+static inline struct drm_plane_state *
+drm_atomic_get_next_plane_state(struct drm_atomic_state *state,
+				struct drm_plane *plane)
+{
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+
+	if (plane_state)
+		return plane_state;
+	return plane->state;
+}
+
 /**
  * drm_atomic_get_existing_connector_state - get connector state, if it exists
  * @state: global atomic state object
-- 
2.37.3