ALSA: usb-audio: fix detection of vendor-specific device protocol settings

The Audio Class v2 support code in 2.6.35 added checks for the
bInterfaceProtocol field.  However, there are devices (usually those
detected by vendor-specific quirks) that do not have one of the
predefined values in this field, which made the driver reject them.

To fix this regression, restore the old behaviour, i.e., assume that
a device with an unknown bInterfaceProtocol field (other than
UAC_VERSION_2) has more or less UAC-v1-compatible descriptors.

[compile warning fixes by tiwai]

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: Daniel Mack <daniel@caiaq.de>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 9 insertions, 1 deletions

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index c166db0057d3..3ed3901369ce 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2175,7 +2175,15 @@ int snd_usb_create_mixer(struct snd_usb_audio *chip, int ctrlif,
         }
 
         host_iface = &usb_ifnum_to_if(chip->dev, ctrlif)->altsetting[0];
-        mixer->protocol = get_iface_desc(host_iface)->bInterfaceProtocol;
+        switch (get_iface_desc(host_iface)->bInterfaceProtocol) {
+        case UAC_VERSION_1:
+        default:
+                mixer->protocol = UAC_VERSION_1;
+                break;
+        case UAC_VERSION_2:
+                mixer->protocol = UAC_VERSION_2;
+                break;
+        }
 
         if ((err = snd_usb_mixer_controls(mixer)) < 0 ||
             (err = snd_usb_mixer_status_create(mixer)) < 0)