From edc08d0a40f7ddab6bf7249e59ecf692d36c7192 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Wed, 6 Nov 2013 13:56:27 -0200 Subject: [PATCH] drm/i915: Fix gen3/4 vblank counter wraparound MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When the hardware frame counter reads 0xffffff and we're already past vblank start, we'd return 0x1000000 as the vblank counter value. Once we'd cross into the next frame's active portion, the vblank counter would wrap to 0. So we're reporting two different vblank counter values for the same frame. Fix the problem by masking the cooked value by 0xffffff to make sure the counter wraps already after vblank start. Signed-off-by: Ville Syrjälä Signed-off-by: Rodrigo Vivi Reviewed-by: Imre Deak Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_irq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index a228176..c6176f3 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -583,7 +583,7 @@ static u32 i915_get_vblank_counter(struct drm_device *dev, int pipe) * Cook up a vblank counter by also checking the pixel * counter against vblank start. */ - return ((high1 << 8) | low) + (pixel >= vbl_start); + return (((high1 << 8) | low) + (pixel >= vbl_start)) & 0xffffff; } static u32 gm45_get_vblank_counter(struct drm_device *dev, int pipe) -- 2.7.4