From: Daniel Vetter <daniel.vetter@ffwll.ch>
Date: Thu, 4 Oct 2012 17:20:03 +0000 (+0200)
Subject: drm/i915: paper over a pipe-enable vs pageflip race
X-Git-Tag: firefly_0821_release~3680^2~1722^2~8^2~18
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=6ce9410047f9f06c1b3336d5215402b77d6fd70f;p=firefly-linux-kernel-4.4.55.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 <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---

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)