[Intel-gfx] [PATCH 16/19] drm: Store the vblank timestamp when adjusting the counter during disable

[Daniel Vetter]

On Wed, Aug 06, 2014 at 02:49:59PM +0300, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> During vblank disable the code tries to guess based on the
> timestamps whether we just missed one vblank or not. And if so
> it increments the counter. However it forgets to store the new
> timestamp to the approriate slot in our timestamp ring buffer.
> So anyone querying the timestamp for the resulting sequence
> number would get a stale timestamp. Fix it up by storing the
> new timestamp.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_irq.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 67507a4..e927e5f 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -203,6 +203,13 @@ static void vblank_disable_and_save(struct drm_device *dev, int crtc)
>  	 * hope for the best.
>  	 */
>  	if ((vblrc > 0) && (abs64(diff_ns) > 1000000)) {

We should use DRM_REDUNDANT_VBLIRQ_THRESH_NS here for symmtry. With that
addressed this is Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> +		/* Store new timestamp in ringbuffer. */
> +		vblanktimestamp(dev, crtc, vblcount + 1) = tvblank;
> +
> +		/* Increment cooked vblank count. This also atomically commits
> +		 * the timestamp computed above.
> +		 */
> +		smp_mb__before_atomic();
>  		atomic_inc(&vblank->count);
>  		smp_mb__after_atomic();
>  	}
> -- 
> 1.8.5.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch