<div dir="ltr">I thought about this one again and opposed to my previous comment now think it's fine, also for drivers without hw vblank counter queries. -mario </div><div class="gmail_extra"> <div class="gmail_quote">On Wed, Aug 6, 2014 at 1:49 PM, <<a href="mailto:ville.syrjala@linux.intel.com" target="_blank">ville.syrjala@linux.intel.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">From: Ville Syrjälä <<a href="mailto:ville.syrjala@linux.intel.com">ville.syrjala@linux.intel.com</a>> If we already have a timestamp for the current vblank counter, don't update it with a new timestmap. Small errors can creep in between two timestamp queries for the same vblank count, which could be confusing to userspace when it queries the timestamp for the same vblank sequence number twice. This problem gets exposed when the vblank disable timer is not used (or is set to expire quickly) and thus we can get multiple vblank disable<->enable transition during the same frame which would all attempt to update the timestamp with the latest estimate. Testcase: igt/kms_flip/flip-vs-expired-vblank Signed-off-by: Ville Syrjälä <<a href="mailto:ville.syrjala@linux.intel.com">ville.syrjala@linux.intel.com</a>> --- drivers/gpu/drm/drm_irq.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index af33df1..0523f5b 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -106,6 +106,9 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc) DRM_DEBUG("enabling vblank interrupts on crtc %d, missed %d\n", crtc, diff); + if (diff == 0) + return; + /* Reinitialize corresponding vblank timestamp if high-precision query * available. Skip this step if query unsupported or failed. Will * reinitialize delayed at next vblank interrupt in that case. -- 1.8.5.5 </blockquote></div> </div>