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Commit 5ceecb2f authored by Michel Dänzer's avatar Michel Dänzer Committed by Daniel Vetter
Browse files

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: default avatarMichel Dänzer <michel.daenzer@amd.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent 60f207a5

drivers/gpu/drm/drm_irq.c

+2 −2
Original line number Diff line number Diff line
@@ -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

	 * 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 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc) 
	/* 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);