[PATCH v2] drm/i915/display: Fix dma_fence_wait_timeout() return value handling

[Matthew Brost]

On Mon, Jul 07, 2025 at 11:16:21AM -0700, Matthew Brost wrote:
> On Mon, Jul 07, 2025 at 05:45:51AM +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.
> > 
> > Signed-off-by: Aakash Deep Sarkar <aakash.deep.sarkar at intel.com>
> 
> Reviewed-by: Matthew Brost <matthew.brost at intel.com>
> 

Opps, missed this. You need a fixes tag so this is backported.

Techincally I guess you only need the tag for the patch that introduced
the Xe driver.

Matt

> > ---
> >  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
> >