From: Ville Syrj?l? <ville.syrj...@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 Syrj?l? <ville.syrjala at 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));
--
1.8.5.5
