[PATCH v3] drm/i915/display: Fix dma_fence_wait_timeout() return value handling

[Matthew Brost]

On Tue, Jul 08, 2025 at 07:33:27AM +0000, Aakash Deep Sarkar wrote:
> dma_fence_wait_timeout returns a long type but the driver is
> only using the lower 32 bits of the retval and discarding the
> upper 32 bits.
> 
> This is particularly problematic if there are already signalled
> or stub fences on some of the hw planes. In this case the
> dma_fence_wait_timeout function will immediately return with
> timeout value MAX_SCHEDULE_TIMEOUT (0x7fffffffffffffff) since
> the fence is already signalled. If the driver only uses the lower
> 32 bits of this return value then it'll interpret it as an error
> code (0xFFFFFFFF or (-1)) and skip the wait on the remaining fences.
> 
> This issue was first observed in the xe driver with the Android
> compositor where the GPU composited layer was not properly waited
> on when there were stub fences in other overlay planes resulting in
> visual artifacts.
> 
> Fixes: d59cf7bb73f3c ("drm/i915/display: Use dma_fence interfaces instead of i915_sw_fence")
> Signed-off-by: Aakash Deep Sarkar <aakash.deep.sarkar at intel.com>

Keep my RB:
Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 456fc4b04cda..7035c1fc9033 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -7092,7 +7092,8 @@ static void intel_atomic_commit_fence_wait(struct intel_atomic_state *intel_stat
>  	struct drm_i915_private *i915 = to_i915(intel_state->base.dev);
>  	struct drm_plane *plane;
>  	struct drm_plane_state *new_plane_state;
> -	int ret, i;
> +	long ret;
> +	int i;
>  
>  	for_each_new_plane_in_state(&intel_state->base, plane, new_plane_state, i) {
>  		if (new_plane_state->fence) {
> -- 
> 2.49.0
>