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drm: Fix off-by-one in vblank hardware counter wraparound handling

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dev->max_vblank_count contains the largest value that can be represented
by the hardware counter. When the hardware counter wraps around, we have
to add that value + 1 to get the same value as if the hardware counter
didn't wrap around.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Michel Dänzer
2015-05-26 17:53:38 +09:00
committed by Daniel Vetter
parent 60f207a5b6
commit 5ceecb2fa7
1 changed files with 2 additions and 2 deletions
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4
drivers/gpu/drm/drm_irq.c
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@@ -130,7 +130,7 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc)
/* /*
* Interrupts were disabled prior to this call, so deal with counter * Interrupts were disabled prior to this call, so deal with counter
* wrap if needed. * wrap if needed.
* NOTE! It's possible we lost a full dev->max_vblank_count events * NOTE! It's possible we lost a full dev->max_vblank_count + 1 events
* here if the register is small or we had vblank interrupts off for * here if the register is small or we had vblank interrupts off for
* a long time. * a long time.
* *
@@ -147,7 +147,7 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc)
/* Deal with counter wrap */ /* Deal with counter wrap */
diff = cur_vblank - vblank->last; diff = cur_vblank - vblank->last;
if (cur_vblank < vblank->last) { if (cur_vblank < vblank->last) {
diff += dev->max_vblank_count; diff += dev->max_vblank_count + 1;
DRM_DEBUG("last_vblank[%d]=0x%x, cur_vblank=0x%x => diff=0x%x\n", DRM_DEBUG("last_vblank[%d]=0x%x, cur_vblank=0x%x => diff=0x%x\n",
crtc, vblank->last, cur_vblank, diff); crtc, vblank->last, cur_vblank, diff);