[PATCH] ALSA: usb-audio: workaround for iface reset issue

[Takashi Iwai]

The recently introduced sample rate validation code seems causing a
problem on some devices; namely, after performing this, the bus gets
screwed and it influences even on other USB devices.
As a quick workaround, perform it only for the necessary devices;
currently MOTU devices are known to need the valid altset checks, so
filter out other devices.

Fixes: 93db51d06b32 ("ALSA: usb-audio: Check valid altsetting at parsing rates for UAC2/3")
Reported-by: Jamie Heilman <jamie at audible.transient.net>
BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1178203
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/format.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sound/usb/format.c b/sound/usb/format.c
index 9ebc5d202c87..e6ff317a6785 100644
--- a/sound/usb/format.c
+++ b/sound/usb/format.c
@@ -466,6 +466,17 @@ static int validate_sample_rate_table_v2v3(struct snd_usb_audio *chip,
 	unsigned int nr_rates;
 	int i, err;
 
+	/* performing the rate verification may lead to unexpected USB bus
+	 * behavior afterwards by some unknown reason.  Do this only for the
+	 * known devices.
+	 */
+	switch (USB_ID_VENDOR(chip->usb_id)) {
+	case 0x07fd: /* MOTU */
+		break;
+	default:
+		return 0; /* don't perform the validation as default */
+	}
+
 	table = kcalloc(fp->nr_rates, sizeof(*table), GFP_KERNEL);
 	if (!table)
 		return -ENOMEM;
-- 
2.26.2