drm: Fix off-by-one in vblank hardware counter wraparound handling
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>
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 1967e7f..6f02b4b 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -130,7 +130,7 @@
/*
* Interrupts were disabled prior to this call, so deal with counter
* 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
* a long time.
*
@@ -147,7 +147,7 @@
/* Deal with counter wrap */
diff = 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",
crtc, vblank->last, cur_vblank, diff);
