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sound: usb-audio: add workaround for Blue Microphones devices 

Blue Microphones USB devices have an alternate setting that sends two
channels of data to the computer.  Unfortunately, the descriptors of
that altsetting have a wrong channel setting, which means that any
recorded data from such a device has twice the sample rate from what
would be expected.

This patch adds a workaround to ignore that altsetting.  Since these
devices have only one actual channel, no data is lost.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Clemens Ladisch 2009-07-13 13:21:58 +02:00 committed by Takashi Iwai
parent 6847e154e3
commit 8886f33f25
1 changed files with 13 additions and 1 deletions
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14
sound/usb/usbaudio.c
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@ -2661,7 +2661,7 @@ static int parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
struct usb_interface_descriptor *altsd;
int i, altno, err, stream;
int format;
struct audioformat *fp;
struct audioformat *fp = NULL;
unsigned char *fmt, *csep;
int num;
@ -2734,6 +2734,18 @@ static int parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
continue;
}
/*
* Blue Microphones workaround: The last altsetting is identical
* with the previous one, except for a larger packet size, but
* is actually a mislabeled two-channel setting; ignore it.
*/
if (fmt[4] == 1 && fmt[5] == 2 && altno == 2 && num == 3 &&
fp && fp->altsetting == 1 && fp->channels == 1 &&
fp->format == SNDRV_PCM_FORMAT_S16_LE &&
le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize) ==
fp->maxpacksize * 2)
continue;
csep = snd_usb_find_desc(alts->endpoint[0].extra, alts->endpoint[0].extralen, NULL, USB_DT_CS_ENDPOINT);
/* Creamware Noah has this descriptor after the 2nd endpoint */
if (!csep && altsd->bNumEndpoints >= 2)