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

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>
This commit is contained in:
Daniel Mack 2010-09-02 17:13:15 +08:00 committed by Takashi Iwai
parent 2bfc96a127
commit 7b6717e144
1 changed files with 7 additions and 1 deletions
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8
sound/usb/card.c
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@ -465,7 +465,13 @@ 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 */