ALSA: snd-usb: fix cross-interface streaming devices

Commit 68e67f40b ("ALSA: snd-usb: move calls to usb_set_interface")
saved us some unnecessary calls to snd_usb_set_interface() but ignored
the fact that there is at least one device out there which operates on
two endpoint in different interfaces simultaniously.

Take care for this by catching the case where data and sync endpoints
are located on different interfaces and calling snd_usb_set_interface()
between the start of the two endpoints.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Reported-by: Robert M. Albrecht <linux@romal.de>
Cc: stable@kernel.org [v3.5+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index e80b6687f43ae3851391e670c1df720dd64d3945..fd5e982fc98c2af6b01f84d00450b1262b76f218 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -236,6 +236,21 @@ static int start_endpoints(struct snd_usb_substream *subs, int can_sleep)
            !test_and_set_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags)) {
                struct snd_usb_endpoint *ep = subs->sync_endpoint;
 
+               if (subs->data_endpoint->iface != subs->sync_endpoint->iface ||
+                   subs->data_endpoint->alt_idx != subs->sync_endpoint->alt_idx) {
+                       err = usb_set_interface(subs->dev,
+                                               subs->sync_endpoint->iface,
+                                               subs->sync_endpoint->alt_idx);
+                       if (err < 0) {
+                               snd_printk(KERN_ERR
+                                          "%d:%d:%d: cannot set interface (%d)\n",
+                                          subs->dev->devnum,
+                                          subs->sync_endpoint->iface,
+                                          subs->sync_endpoint->alt_idx, err);
+                               return -EIO;
+                       }
+               }
+
                snd_printdd(KERN_DEBUG "Starting sync EP @%p\n", ep);
 
                ep->sync_slave = subs->data_endpoint;