[PATCH] drm/amd/display: Fix mem_type change detection for async flips

[Matthew Schwartz <matthew.schwartz@linux.dev>]

[Why]
amdgpu_dm_crtc_mem_type_changed() fetches the "old" and "new" plane state
with two drm_atomic_get_plane_state() calls, which both return the new
state. It compares a state against itself, so it never detects a mem_type
change and never rejects the async flip.

On DCN 3.0.1, this shows up as intermittent corruption when a single DCC
plane is scanned out with immediate flips under gamescope and its buffer
moves between the VRAM carveout and GTT.

[How]
Use drm_atomic_get_old_plane_state() and drm_atomic_get_new_plane_state()
to compare the actual old and new states. These return NULL rather than
an error pointer for a plane that is not part of the commit, so the
IS_ERR() check becomes a NULL check that skips those planes, such as an
unmodified cursor still in the CRTC's plane_mask.

Fixes: 4caacd1671b7a ("drm/amd/display: Do not elevate mem_type change to full update")
Signed-off-by: Matthew Schwartz <matthew.schwartz@linux.dev>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 6c1e7e13f0399..711640739179e 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -12934,13 +12934,11 @@ static bool amdgpu_dm_crtc_mem_type_changed(struct drm_device *dev,
 	struct drm_plane_state *new_plane_state, *old_plane_state;
 
 	drm_for_each_plane_mask(plane, dev, crtc_state->plane_mask) {
-		new_plane_state = drm_atomic_get_plane_state(state, plane);
-		old_plane_state = drm_atomic_get_plane_state(state, plane);
+		new_plane_state = drm_atomic_get_new_plane_state(state, plane);
+		old_plane_state = drm_atomic_get_old_plane_state(state, plane);
 
-		if (IS_ERR(new_plane_state) || IS_ERR(old_plane_state)) {
-			drm_err(dev, "Failed to get plane state for plane %s\n", plane->name);
-			return false;
-		}
+		if (!old_plane_state || !new_plane_state)
+			continue;
 
 		if (old_plane_state->fb && new_plane_state->fb &&
 		    get_mem_type(old_plane_state->fb) != get_mem_type(new_plane_state->fb))
-- 
2.54.0