[PATCH 17/19] drm/i915: Clear .last vblank count before drm_vblank_off() when sanitizing crtc state

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

We call drm_vblank_off() during crtc sanitation to make sure the
software and hardware states agree. However drm_vblank_off() will
try to update the vblank timestamp and sequence number which lands
us in some trouble.

As the pipe is disabled the hardware frame counter query will
return 0. If the .last doesn't match the code will try to add the
difference to the user visible sequence number. During driver init
that's OK as .last == 0, but during resume .last may be anything.
So we should make sure we don't try to apply the diff here by zeroing
.last beforehand. Otherwise there maybe be a random jump in the user
visible sequence number across suspend.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ae5f20d..c00bcd0 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12918,8 +12918,11 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
 	/* restore vblank interrupts to correct state */
 	if (crtc->active)
 		drm_vblank_on(dev, crtc->pipe);
-	else
+	else {
+		/* avoid random jumps in seq/ts */
+		dev->vblank[crtc->pipe].last = 0;
 		drm_vblank_off(dev, crtc->pipe);
+	}
 
 	/* We need to sanitize the plane -> pipe mapping first because this will
 	 * disable the crtc (and hence change the state) if it is wrong. Note
-- 
1.8.5.5