+bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ u16 bufs;
+
+ START_USE(vq);
+
+ /* We optimistically turn back on interrupts, then check if there was
+ * more to do. */
+ /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
+ * either clear the flags bit or point the event index at the next
+ * entry. Always do both to keep code simple. */
+ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ /* TODO: tune this threshold */
+ bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
+ vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
+ virtio_mb();
+ if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
+ END_USE(vq);
+ return false;
+ }
+
+ END_USE(vq);
+ return true;
+}
+EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
+