[media] em28xx: fix check for audio only usb interfaces when changing…

… the usb alternate setting

Previously, we've been assuming that the video endpoints are always at usb
interface 0. Hence, if vendor audio endpoints are provided at a separate
interface, they were supposed to be at interface number > 0.
Instead of checking for (interface number > 0) to determine if an interface
is a pure audio interface, dev->is_audio_only should be checked.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx-audio.c

@@ -266,18 +266,29 @@ static int snd_em28xx_capture_open(struct snd_pcm_substream *substream)
 	dprintk("opening device and trying to acquire exclusive lock\n");
 
 	runtime->hw = snd_em28xx_hw_capture;
-	if ((dev->alt == 0 || dev->ifnum) && dev->adev.users == 0) {
+	if ((dev->alt == 0 || dev->is_audio_only) && dev->adev.users == 0) {
 		int nonblock = !!(substream->f_flags & O_NONBLOCK);
 
 		if (nonblock) {
 			if (!mutex_trylock(&dev->lock))
 				return -EAGAIN;
 		} else
 			mutex_lock(&dev->lock);
-		if (dev->ifnum)
+		if (dev->is_audio_only)
+			/* vendor audio is on a separate interface */
 			dev->alt = 1;
 		else
+			/* vendor audio is on the same interface as video */
 			dev->alt = 7;
+			/*
+			 * FIXME: The intention seems to be to select the alt
+			 * setting with the largest wMaxPacketSize for the video
+			 * endpoint.
+			 * At least dev->alt should be used instead, but we
+			 * should probably not touch it at all if it is
+			 * already >0, because wMaxPacketSize of the audio
+			 * endpoints seems to be the same for all.
+			 */
 
 		dprintk("changing alternate number on interface %d to %d\n",
 			dev->ifnum, dev->alt);