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authorVille Syrjälä <ville.syrjala@linux.intel.com>2014-08-06 15:49:49 +0400
committerDaniel Vetter <daniel.vetter@ffwll.ch>2014-08-07 00:39:25 +0400
commitf8ad028cc033f75fc479ca1c30e2ea4ba56e5269 (patch)
tree57a183cb4277f706bccdcd0e48d22a72537913fa /drivers/gpu/drm/drm_irq.c
parent812e7465a7decf3cca0b5f71977a25eecd9626a4 (diff)
downloadlinux-f8ad028cc033f75fc479ca1c30e2ea4ba56e5269.tar.xz
drm: Avoid random vblank counter jumps if the hardware counter has been reset
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. Reviewed-by: Matt Roper <matthew.d.roper@intel.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Diffstat (limited to 'drivers/gpu/drm/drm_irq.c')
-rw-r--r--drivers/gpu/drm/drm_irq.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 1f86f6c6ecc6..fc1525a499d9 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));