dmaengine: virt-dma: add support for cyclic DMA periodic callbacks

Add support for cyclic DMA's periodic callbacks.  Drivers are expected
to call vchan_cyclic_callback() when a period has completed, which will
schedule the tasklet to make the callback into the driver.

As callbacks are made from tasklet context, it is important to realise
that we don't guarantee a callback for each completed period, but for
N completed periods where N may be greater than one.

Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 15 insertions, 4 deletions

diff --git a/drivers/dma/virt-dma.c b/drivers/dma/virt-dma.c
index a8054fc40cef..6f80432a3f0a 100644
--- a/drivers/dma/virt-dma.c
+++ b/drivers/dma/virt-dma.c
@@ -59,17 +59,28 @@ EXPORT_SYMBOL_GPL(vchan_find_desc);
 static void vchan_complete(unsigned long arg)
 {
 	struct virt_dma_chan *vc = (struct virt_dma_chan *)arg;
+	struct virt_dma_desc *vd;
+	dma_async_tx_callback cb = NULL;
+	void *cb_data = NULL;
 	LIST_HEAD(head);
 
 	spin_lock_irq(&vc->lock);
 	list_splice_tail_init(&vc->desc_completed, &head);
+	vd = vc->cyclic;
+	if (vd) {
+		vc->cyclic = NULL;
+		cb = vd->tx.callback;
+		cb_data = vd->tx.callback_param;
+	}
 	spin_unlock_irq(&vc->lock);
 
+	if (cb)
+		cb(cb_data);
+
 	while (!list_empty(&head)) {
-		struct virt_dma_desc *vd = list_first_entry(&head,
-				struct virt_dma_desc, node);
-		dma_async_tx_callback cb = vd->tx.callback;
-		void *cb_data = vd->tx.callback_param;
+		vd = list_first_entry(&head, struct virt_dma_desc, node);
+		cb = vd->tx.callback;
+		cb_data = vd->tx.callback_param;
 
 		list_del(&vd->node);