[ALSA] usb audio: Fix another Dallas quirk

Dallas USB speakers are buggy in more than one way. One of configs
they offer does not work at all.

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 12 insertions, 1 deletions

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 5c40c031dd57..ff2e09a46133 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -2676,12 +2676,23 @@ static int parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
         int format;
         struct audioformat *fp;
         unsigned char *fmt, *csep;
+        int num;
 
         dev = chip->dev;
 
         /* parse the interface's altsettings */
         iface = usb_ifnum_to_if(dev, iface_no);
-        for (i = 0; i < iface->num_altsetting; i++) {
+
+        num = iface->num_altsetting;
+
+        /*
+         * Dallas DS4201 workaround: It presents 5 altsettings, but the last
+         * one misses syncpipe, and does not produce any sound.
+         */
+        if (chip->usb_id == USB_ID(0x04fa, 0x4201))
+                num = 4;
+
+        for (i = 0; i < num; i++) {
                 alts = &iface->altsetting[i];
                 altsd = get_iface_desc(alts);
                 /* skip invalid one */