On Wed, Aug 06, 2014 at 02:56:14PM +0200, Daniel Vetter wrote:
On Wed, Aug 06, 2014 at 02:49:57PM +0300, ville.syrjala@linux.intel.com wrote:
From: Ville Syrjälä ville.syrjala@linux.intel.com
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 ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
On second consideration this seems to just paper over drivers that enable vblanks a few too many times. Or a bug in the vblank_get handling in drm_irq.c. If it's just that I think we should just tighten up the checks to catch that and drop this patch here. -Daniel
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
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-- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch