ALSA: usb-audio: Assume first control interface is for audio

commit 7b6717e144de6592e614fd7fc3b914b6bf686a9d upstream.

For devices with more than one control interface, let's assume the first
one contains the audio controls. Unfortunately, there is no field in any
of the descriptors to tell us whether a control interface is for audio
or MIDI controls, so a better check is not easy to implement.

On a composite device with audio and MIDI functions, for example, the
code currently overwrites chip->ctrl_intf, causing operations on the
control interface to fail if they are issued after the device probe.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/sound/usb/card.c b/sound/usb/card.c
index d1924d71681611ee64f05da7979c855ec5411ee5..ceeba8918454f075b1ce6bef0c704734616688ac 100644 (file)
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -466,7 +466,13 @@ static void *snd_usb_audio_probe(struct usb_device *dev,
                        goto __error;
        }
 
-       chip->ctrl_intf = alts;
+       /*
+        * For devices with more than one control interface, we assume the
+        * first contains the audio controls. We might need a more specific
+        * check here in the future.
+        */
+       if (!chip->ctrl_intf)
+               chip->ctrl_intf = alts;
 
        if (err > 0) {
                /* create normal USB audio interfaces */