From: Daniel Vetter Date: Thu, 4 Oct 2012 17:20:03 +0000 (+0200) Subject: drm/i915: paper over a pipe-enable vs pageflip race X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=6ce9410047f9f06c1b3336d5215402b77d6fd70f;p=openwrt%2Fstaging%2Fblogic.git drm/i915: paper over a pipe-enable vs pageflip race 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. Note that this is empirical duct-tape: I've noticed that we seem to only ever miss the very first vblank irq right after enabling the pipe. And with this hack applied I couldn't reproduce the failure case anywhere else any more. Tested-by: Imre Deak Reviewed-by: Imre Deak Signed-off-by: Daniel Vetter --- diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 67912febb322..9cecfd73b0b1 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)