+
+/**
+ * async_tx_channel_switch - queue an interrupt descriptor with a dependency
+ * pre-attached.
+ * @depend_tx: the operation that must finish before the new operation runs
+ * @tx: the new operation
+ */
+static void
+async_tx_channel_switch(struct dma_async_tx_descriptor *depend_tx,
+ struct dma_async_tx_descriptor *tx)
+{
+ struct dma_chan *chan;
+ struct dma_device *device;
+ struct dma_async_tx_descriptor *intr_tx = (void *) ~0;
+
+ /* first check to see if we can still append to depend_tx */
+ spin_lock_bh(&depend_tx->lock);
+ if (depend_tx->parent && depend_tx->chan == tx->chan) {
+ tx->parent = depend_tx;
+ depend_tx->next = tx;
+ intr_tx = NULL;
+ }
+ spin_unlock_bh(&depend_tx->lock);
+
+ if (!intr_tx)
+ return;
+
+ chan = depend_tx->chan;
+ device = chan->device;
+
+ /* see if we can schedule an interrupt
+ * otherwise poll for completion
+ */
+ if (dma_has_cap(DMA_INTERRUPT, device->cap_mask))
+ intr_tx = device->device_prep_dma_interrupt(chan);
+ else
+ intr_tx = NULL;
+
+ if (intr_tx) {
+ intr_tx->callback = NULL;
+ intr_tx->callback_param = NULL;
+ tx->parent = intr_tx;
+ /* safe to set ->next outside the lock since we know we are
+ * not submitted yet
+ */
+ intr_tx->next = tx;
+
+ /* check if we need to append */
+ spin_lock_bh(&depend_tx->lock);
+ if (depend_tx->parent) {
+ intr_tx->parent = depend_tx;
+ depend_tx->next = intr_tx;
+ async_tx_ack(intr_tx);
+ intr_tx = NULL;
+ }
+ spin_unlock_bh(&depend_tx->lock);
+
+ if (intr_tx) {
+ intr_tx->parent = NULL;
+ intr_tx->tx_submit(intr_tx);
+ async_tx_ack(intr_tx);
+ }
+ } else {
+ if (dma_wait_for_async_tx(depend_tx) == DMA_ERROR)
+ panic("%s: DMA_ERROR waiting for depend_tx\n",
+ __func__);
+ tx->tx_submit(tx);
+ }
+}
+
+
+/**
+ * submit_disposition - while holding depend_tx->lock we must avoid submitting
+ * new operations to prevent a circular locking dependency with
+ * drivers that already hold a channel lock when calling
+ * async_tx_run_dependencies.
+ * @ASYNC_TX_SUBMITTED: we were able to append the new operation under the lock
+ * @ASYNC_TX_CHANNEL_SWITCH: when the lock is dropped schedule a channel switch
+ * @ASYNC_TX_DIRECT_SUBMIT: when the lock is dropped submit directly
+ */
+enum submit_disposition {
+ ASYNC_TX_SUBMITTED,
+ ASYNC_TX_CHANNEL_SWITCH,
+ ASYNC_TX_DIRECT_SUBMIT,
+};
+