[PATCH] ALSA: usb-audio: Workaround for clock setup on TEAC devices

[Takashi Iwai]

Maris reported that TEAC UD-501 (0644:8043) doesn't work with the
typical "clock source 41 is not valid, cannot use" errors on the
recent kernels.  The currently known workaround so far is to restore
(partially) what we've done unconditionally at the clock setup;
namely, re-setup the USB interface immediately after the clock is
changed.  This patch re-introduces the behavior conditionally for TEAC
devices.

Further notes:
- The USB interface shall be set later in
  snd_usb_endpoint_configure(), but this seems to be too late.
- Even calling  usb_set_interface() right after
  sne_usb_init_sample_rate() doesn't help; so this must be related
  with the clock validation, too.
- The device may still spew the "clock source 41 is not valid" error
  at the first clock setup.  This seems happening at the very first
  try of clock setup, but it disappears at later attempts.
  The error is likely harmless because the driver retries the clock
  setup (such an error is more or less expected on some devices).

Fixes: bf6313a0ff76 ("ALSA: usb-audio: Refactor endpoint management")
Reported-and-tested-by: Maris Abele <maris7abele at gmail.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/clock.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 4dfe76416794..3c435d379306 100644
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -572,6 +572,13 @@ static int set_sample_rate_v2v3(struct snd_usb_audio *chip,
 		/* continue processing */
 	}
 
+	/* FIXME - TEAC devices require the immediate interface setup */
+	if (rate != prev_rate && USB_ID_VENDOR(chip->usb_id) == 0x0644) {
+		usb_set_interface(chip->dev, fmt->iface, fmt->altsetting);
+		if (chip->quirk_flags & QUIRK_FLAG_IFACE_DELAY)
+			msleep(50);
+	}
+
 validation:
 	/* validate clock after rate change */
 	if (!uac_clock_source_is_valid(chip, fmt, clock))
-- 
2.35.3