dmaengine: rcar-dmac: Check the done lists in rcar_dmac_chan_get_residue()

This patch fixes an issue that a race condition happens between a client driver and the rcar-dmac driver:

- The rcar_dmac_isr_transfer_end() is called.
- The done list appears, and desc.running is the next active list.
- rcar_dmac_chan_get_residue() is called by a client driver before rcar_dmac_isr_channel_thread() is called.
- The rcar_dmac_chan_get_residue() will not find any descriptors.
- And, the following WARNING happens:

	WARN(1, "No descriptor for cookie!");

The sh-sci driver with HSCIF (921,600bps) on R-Car H3 can cause this situation.
So, this patch checks the done lists in rcar_dmac_chan_get_residue() and returns zero if the done lists has the argument cookie.

Tested-by Nguyen Viet Dung <[email protected]>

Signed-off-by Yoshihiro Shimoda <[email protected]>

---
 drivers/dma/sh/rcar-dmac.c | 9 +++++++++
 1 file changed, 9 insertions(+)

drivers/dma/sh/rcar-dmac.c +9 -0

index 2b2c7db..f748be6 100644
@@ -1264,8 +1264,17 @@ static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 	 * If the cookie doesn't correspond to the currently running transfer
 	 * then the descriptor hasn't been processed yet, and the residue is
 	 * equal to the full descriptor size.
+	 * Also, a client driver is possible to call this function before
+	 * rcar_dmac_isr_channel_thread() runs. In this case, the "desc.running"
+	 * will be the next descriptor, and the done list will appear. So, if
+	 * the argument cookie matches the done list's cookie, we can assume
+	 * the residue is zero.
 	 */
 	if (cookie != desc->async_tx.cookie) {
+		list_for_each_entry(desc, &chan->desc.done, node) {
+			if (cookie == desc->async_tx.cookie)
+				return 0;
+		}
 		list_for_each_entry(desc, &chan->desc.pending, node) {
 			if (cookie == desc->async_tx.cookie)
 				return desc->size;

Signature · 1 line

1.9.1