+/**
+ * drm_vblank_count - retrieve "cooked" vblank counter value
+ * @dev: DRM device
+ * @crtc: which counter to retrieve
+ *
+ * Fetches the "cooked" vblank count value that represents the number of
+ * vblank events since the system was booted, including lost events due to
+ * modesetting activity.
+ */
+u32 drm_vblank_count(struct drm_device *dev, int crtc)
+{
+ return atomic_read(&dev->_vblank_count[crtc]);
+}
+EXPORT_SYMBOL(drm_vblank_count);
+
+/**
+ * drm_update_vblank_count - update the master vblank counter
+ * @dev: DRM device
+ * @crtc: counter to update
+ *
+ * Call back into the driver to update the appropriate vblank counter
+ * (specified by @crtc). Deal with wraparound, if it occurred, and
+ * update the last read value so we can deal with wraparound on the next
+ * call if necessary.
+ *
+ * Only necessary when going from off->on, to account for frames we
+ * didn't get an interrupt for.
+ *
+ * Note: caller must hold dev->vbl_lock since this reads & writes
+ * device vblank fields.
+ */
+static void drm_update_vblank_count(struct drm_device *dev, int crtc)
+{
+ u32 cur_vblank, diff;
+
+ /*
+ * 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
+ * here if the register is small or we had vblank interrupts off for
+ * a long time.
+ */
+ cur_vblank = dev->driver->get_vblank_counter(dev, crtc);
+ diff = cur_vblank - dev->last_vblank[crtc];
+ if (cur_vblank < dev->last_vblank[crtc]) {
+ diff += dev->max_vblank_count;
+
+ DRM_DEBUG("last_vblank[%d]=0x%x, cur_vblank=0x%x => diff=0x%x\n",
+ crtc, dev->last_vblank[crtc], cur_vblank, diff);
+ }
+
+ DRM_DEBUG("enabling vblank interrupts on crtc %d, missed %d\n",
+ crtc, diff);
+
+ atomic_add(diff, &dev->_vblank_count[crtc]);
+}
+
+/**
+ * drm_vblank_get - get a reference count on vblank events
+ * @dev: DRM device
+ * @crtc: which CRTC to own
+ *
+ * Acquire a reference count on vblank events to avoid having them disabled
+ * while in use.
+ *
+ * RETURNS
+ * Zero on success, nonzero on failure.
+ */
+int drm_vblank_get(struct drm_device *dev, int crtc)
+{
+ unsigned long irqflags;
+ int ret = 0;
+
+ spin_lock_irqsave(&dev->vbl_lock, irqflags);
+ /* Going from 0->1 means we have to enable interrupts again */
+ if (atomic_add_return(1, &dev->vblank_refcount[crtc]) == 1 &&
+ !dev->vblank_enabled[crtc]) {
+ ret = dev->driver->enable_vblank(dev, crtc);
+ DRM_DEBUG("enabling vblank on crtc %d, ret: %d\n", crtc, ret);
+ if (ret)
+ atomic_dec(&dev->vblank_refcount[crtc]);
+ else {
+ dev->vblank_enabled[crtc] = 1;
+ drm_update_vblank_count(dev, crtc);
+ }
+ }
+ spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+
+ return ret;
+}
+EXPORT_SYMBOL(drm_vblank_get);
+
+/**
+ * drm_vblank_put - give up ownership of vblank events
+ * @dev: DRM device
+ * @crtc: which counter to give up
+ *
+ * Release ownership of a given vblank counter, turning off interrupts
+ * if possible.
+ */
+void drm_vblank_put(struct drm_device *dev, int crtc)
+{
+ /* Last user schedules interrupt disable */
+ if (atomic_dec_and_test(&dev->vblank_refcount[crtc]))
+ mod_timer(&dev->vblank_disable_timer, jiffies + 5*DRM_HZ);
+}
+EXPORT_SYMBOL(drm_vblank_put);
+
+/**
+ * drm_modeset_ctl - handle vblank event counter changes across mode switch
+ * @DRM_IOCTL_ARGS: standard ioctl arguments
+ *
+ * Applications should call the %_DRM_PRE_MODESET and %_DRM_POST_MODESET
+ * ioctls around modesetting so that any lost vblank events are accounted for.
+ *
+ * Generally the counter will reset across mode sets. If interrupts are
+ * enabled around this call, we don't have to do anything since the counter
+ * will have already been incremented.
+ */
+int drm_modeset_ctl(struct drm_device *dev, void *data,
+ struct drm_file *file_priv)
+{
+ struct drm_modeset_ctl *modeset = data;
+ unsigned long irqflags;
+ int crtc, ret = 0;
+
+ /* If drm_vblank_init() hasn't been called yet, just no-op */
+ if (!dev->num_crtcs)
+ goto out;
+
+ crtc = modeset->crtc;
+ if (crtc >= dev->num_crtcs) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ /*
+ * To avoid all the problems that might happen if interrupts
+ * were enabled/disabled around or between these calls, we just
+ * have the kernel take a reference on the CRTC (just once though
+ * to avoid corrupting the count if multiple, mismatch calls occur),
+ * so that interrupts remain enabled in the interim.
+ */
+ switch (modeset->cmd) {
+ case _DRM_PRE_MODESET:
+ if (!dev->vblank_inmodeset[crtc]) {
+ dev->vblank_inmodeset[crtc] = 1;
+ drm_vblank_get(dev, crtc);
+ }
+ break;
+ case _DRM_POST_MODESET:
+ if (dev->vblank_inmodeset[crtc]) {
+ spin_lock_irqsave(&dev->vbl_lock, irqflags);
+ dev->vblank_disable_allowed = 1;
+ dev->vblank_inmodeset[crtc] = 0;
+ spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+ drm_vblank_put(dev, crtc);
+ }
+ break;
+ default:
+ ret = -EINVAL;
+ break;
+ }
+
+out:
+ return ret;
+}
+