From: Ville Syrjälä ville.syrjala@linux.intel.com
When drm_vblank_on() is called the hardware vblank counter may have been reset, so we can't trust that the old values sampled prior to drm_vblank_off() have anything to do with the new values.
So update the .last count in drm_vblank_on() to make the first drm_vblank_enable() consider that as the reference point. This will correct the user space visible counter to account for the time between drm_vblank_on() and the first drm_vblank_enable() calls.
For extra safety subtract one from the .last count in drm_vblank_on() to make sure that user space will never see the same counter value before and after modeset.
Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com --- drivers/gpu/drm/drm_irq.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index bb64f0f..54cb85d 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -1095,6 +1095,18 @@ void drm_vblank_on(struct drm_device *dev, int crtc) atomic_dec(&dev->vblank[crtc].refcount); dev->vblank[crtc].inmodeset = 0; } + + /* + * sample the current counter to avoid random jumps + * when drm_vblank_enable() applies the diff + * + * -1 to make sure user will never see the same + * vblank counter value before and after a modeset + */ + dev->vblank[crtc].last = + (dev->driver->get_vblank_counter(dev, crtc) - 1) & + dev->max_vblank_count; + /* re-enable interrupts if there's are users left */ if (atomic_read(&dev->vblank[crtc].refcount) != 0) WARN_ON(drm_vblank_enable(dev, crtc));