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

commit 8886f33f25083a47d5fa24ad7b57bb708c5c5403 upstream.

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

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index c10e476226cd0d78dfda35e818950e7c5f10461a..915a1316724ccd586431a14c336ece8346493e35 100644 (file)
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -2674,7 +2674,7 @@ 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;
 
@@ -2747,6 +2747,18 @@ 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)