From: "Pandiyan, Dhinakaran" <>

drm_vblank_count() has an u32 type returning what is a 64-bit vblank count.
The effect of this is when drm_wait_vblank_ioctl() tries to widen the user
space requested vblank sequence using this clipped 32-bit count(when the
value is >= 2^32) as reference, the requested sequence remains a 32-bit
value and gets queued like that. However, the code that checks if the
requested sequence has passed compares this against the 64-bit vblank

With drm_vblank_count() returning all bits of the vblank count, update
drm_crtc_accurate_vblank_count() so that drm_crtc_arm_vblank_event() queues
the correct sequence. Otherwise, this leads to prolonged waits for a vblank
sequence when the current count is >=2^32.

Finally, fix drm_wait_one_vblank() too.

v2: Commit message fix (Keith)
    Squash commits (Rodrigo)

Fixes: 570e86963a51 ("drm: Widen vblank count to 64-bits [v3]")
Cc: Keith Packard <>
Cc: Michel Dänzer <>
Cc: Daniel Vetter <>
Cc: Rodrigo Vivi <>
Signed-off-by: Dhinakaran Pandiyan <>
Acked-by: Daniel Vetter <>
 drivers/gpu/drm/drm_vblank.c | 8 ++++----
 include/drm/drm_vblank.h     | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 32d9bcf5be7f..f0d3ed5f2528 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -271,7 +271,7 @@ static void drm_update_vblank_count(struct drm_device *dev, 
unsigned int pipe,
        store_vblank(dev, pipe, diff, t_vblank, cur_vblank);
-static u32 drm_vblank_count(struct drm_device *dev, unsigned int pipe)
+static u64 drm_vblank_count(struct drm_device *dev, unsigned int pipe)
        struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
@@ -292,11 +292,11 @@ static u32 drm_vblank_count(struct drm_device *dev, 
unsigned int pipe)
  * This is mostly useful for hardware that can obtain the scanout position, but
  * doesn't have a hardware frame counter.
-u32 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)
+u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)
        struct drm_device *dev = crtc->dev;
        unsigned int pipe = drm_crtc_index(crtc);
-       u32 vblank;
+       u64 vblank;
        unsigned long flags;
        WARN_ONCE(drm_debug & DRM_UT_VBL && !dev->driver->get_vblank_timestamp,
@@ -1055,7 +1055,7 @@ void drm_wait_one_vblank(struct drm_device *dev, unsigned 
int pipe)
        struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
        int ret;
-       u32 last;
+       u64 last;
        if (WARN_ON(pipe >= dev->num_crtcs))
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 848b463a0af5..a4c3b0a0a197 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -179,7 +179,7 @@ void drm_crtc_wait_one_vblank(struct drm_crtc *crtc);
 void drm_crtc_vblank_off(struct drm_crtc *crtc);
 void drm_crtc_vblank_reset(struct drm_crtc *crtc);
 void drm_crtc_vblank_on(struct drm_crtc *crtc);
-u32 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc);
+u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc);
 bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
                                           unsigned int pipe, int *max_error,

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