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> --- 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) -- 1.7.10.4
