[Intel-gfx] [PATCH] drm/i915: paper over a pipe-enable vs pageflip race

[Imre Deak]

On Thu, 2012-10-04 at 19:20 +0200, Daniel Vetter wrote:
> I've discovered this on my ivb machine while stress-testing the new
> flip_tests. Only harmful effect observed is that the timestamp is a
> bit bogus.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

I've seen the same issue on an ivb ultrabook machine and the patch gets
rid of it, so:

Tested-by: Imre Deak <imre.deak at intel.com>

> ---
>  drivers/gpu/drm/i915/intel_display.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 67912fe..9cecfd7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3253,6 +3253,16 @@ static void ironlake_crtc_enable(struct drm_crtc *crtc)
>  
>  	if (HAS_PCH_CPT(dev))
>  		intel_cpt_verify_modeset(dev, intel_crtc->pipe);
> +
> +	/*
> +	 * There seems to be a race in PCH platform hw (at least on some
> +	 * outputs) where an enabled pipe still completes any pageflip right
> +	 * away (as if the pipe is off) instead of waiting for vblank. As soon
> +	 * as the first vblank happend, everything works as expected. Hence just
> +	 * wait for one vblank before returning to avoid strange things
> +	 * happening.
> +	 */
> +	intel_wait_for_vblank(dev, intel_crtc->pipe);
>  }
>  
>  static void ironlake_crtc_disable(struct drm_crtc *crtc)