Patch "usb: musb: cppi41: don't check early-TX-interrupt for Isoch transfer" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

usb: musb: cppi41: don't check early-TX-interrupt for Isoch transfer

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-musb-cppi41-don-t-check-early-tx-interrupt-for-isoch-transfer.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Bin Liu <[email protected]>
Date: Fri, 10 Mar 2017 14:43:35 -0600
Subject: usb: musb: cppi41: don't check early-TX-interrupt for Isoch transfer

From: Bin Liu <[email protected]>

commit 0090114d336a9604aa2d90bc83f20f7cd121b76c upstream.

The CPPI 4.1 driver polls register to workaround the premature TX interrupt issue, but it causes audio playback underrun when triggered in Isoch transfers.

Isoch doesn't do back-to-back transfers, the TX should be done by the time the next transfer is scheduled. So skip this polling workaround for Isoch transfer.

---
 drivers/usb/musb/musb_cppi41.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

@@ -232,8 +232,27 @@ static void cppi41_dma_callback(void *pr
 			transferred < cppi41_channel->packet_sz)
 		cppi41_channel->prog_len = 0;
 
-	if (cppi41_channel->is_tx)
-		empty = musb_is_tx_fifo_empty(hw_ep);
+	if (cppi41_channel->is_tx) {
+		u8 type;
+
+		if (is_host_active(musb))
+			type = hw_ep->out_qh->type;
+		else
+			type = hw_ep->ep_in.type;
+
+		if (type == USB_ENDPOINT_XFER_ISOC)
+			/*
+			 * Don't use the early-TX-interrupt workaround below
+			 * for Isoch transfter. Since Isoch are periodic
+			 * transfer, by the time the next transfer is
+			 * scheduled, the current one should be done already.
+			 *
+			 * This avoids audio playback underrun issue.
+			 */
+			empty = true;
+		else
+			empty = musb_is_tx_fifo_empty(hw_ep);
+	}
 
 	if (!cppi41_channel->is_tx || empty) {
 		cppi41_trans_done(cppi41_channel);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/usb-musb-cppi41-don-t-check-early-tx-interrupt-for-isoch-transfer.patch