[PATCH 3.16 264/366] usb: gadget: u_audio: update hw_ptr in iso_complete after data copied

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Joshua Frkuska <joshua_frkuska@xxxxxxxxxx>

commit 6b37bd78d30c890e575a1bda22978d1d2a233362 upstream.

In u_audio_iso_complete, the runtime hw_ptr is updated before the
data is actually copied over to/from the buffer/dma area. When
ALSA uses this hw_ptr, the data may not actually be available to
be used. This causes trash/stale audio to play/record. This
patch updates the hw_ptr after the data has been copied to avoid
this.

Fixes: 132fcb460839 ("usb: gadget: Add Audio Class 2.0 Driver")
Signed-off-by: Joshua Frkuska <joshua_frkuska@xxxxxxxxxx>
Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - Don't use a local hw_ptr variable
 - Adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/usb/gadget/f_uac2.c
+++ b/drivers/usb/gadget/f_uac2.c
@@ -229,12 +229,16 @@ agdev_iso_complete(struct usb_ep *ep, st
 	if (pending >= prm->period_size)
 		update_alsa = true;
 
-	prm->hw_ptr = (prm->hw_ptr + req->actual) % prm->dma_bytes;
-
 	spin_unlock_irqrestore(&prm->lock, flags);
 
 	/* Pack USB load in ALSA ring buffer */
 	memcpy(dst, src, req->actual);
+
+	spin_lock_irqsave(&prm->lock, flags);
+	/* update hw_ptr after data is copied to memory */
+	prm->hw_ptr = (prm->hw_ptr + req->actual) % prm->dma_bytes;
+	spin_unlock_irqrestore(&prm->lock, flags);
+
 exit:
 	if (usb_ep_queue(ep, req, GFP_ATOMIC))
 		dev_err(&uac2->pdev.dev, "%d Error!\n", __LINE__);