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

[Melissa Wen <mwen@igalia.com>]

On 04/06/2026 08:44, Matthew Schwartz wrote:
> [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.

Nice catch!

Reviewed-by: Melissa Wen <mwen@igalia.com>

>
> 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))