drm/msm: Avoid rounding down to zero jiffies

If userspace asked for a timeout greater than zero, but less than a
jiffy, they clearly weren't planning on spinning.  So it is better
to round up to one.

This fixes an issue with supertuxkart that was (for some reason)
spinning on a gl sync with 1ms timeout.  CPU time for a demo lap
drops from:

  15.83user 20.98system 0:47.46elapsed 77%CPU

drops to:

  8.84user 2.30system 0:46.67elapsed 23%CPU

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/528725/
Link: https://lore.kernel.org/r/20230324220013.191795-1-robdclark@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index 9f0c184..7936aa6 100644 (file)
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -548,7 +548,7 @@ static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
                remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
        }
 
-       return clamp(remaining_jiffies, 0LL, (s64)INT_MAX);
+       return clamp(remaining_jiffies, 1LL, (s64)INT_MAX);
 }
 
 /* Driver helpers */