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From:   John Keeping <john@metanate.com>
To:     alsa-devel@alsa-project.org
Cc:     John Keeping <john@metanate.com>, Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, linux-kernel@vger.kernel.org
Subject: [PATCH v2] ALSA: usb-audio: Add quirk for Tascam Model 12
Date:   Tue, 29 Nov 2022 13:00:59 +0000
Message-Id: <20221129130100.1257904-1-john@metanate.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Tascam's Model 12 is a mixer which can also operate as a USB audio
interface.  The audio interface uses explicit feedback but it seems that
it does not correctly handle missing isochronous frames.

When injecting an xrun (or doing anything else that pauses the playback
stream) the feedback rate climbs (for example, at 44,100Hz nominal, I
see a stable rate around 44,099 but xrun injection sees this peak at
around 44,135 in most cases) and glitches are heard in the audio stream
for several seconds - this is significantly worse than the single glitch
expected for an underrun.

While the stream does normally recover and the feedback rate returns to
a stable value, I have seen some occurrences where this does not happen
and the rate continues to increase while no audio is heard from the
output.  I have not found a solid reproduction for this.

This misbehaviour can be avoided by totally resetting the stream state
by switching the interface to alt 0 and back before restarting the
playback stream.

Add a new quirk flag which forces the endpoint and interface to be
reconfigured whenever the stream is stopped, and use this for the Tascam
Model 12.

Separate interfaces are used for the playback and capture endpoints, so
resetting the playback interface here will not affect the capture stream
if it is running.  While there are two endpoints on the interface,
these are the OUT data endpoint and the IN explicit feedback endpoint
corresponding to it and these are always stopped and started together.

Signed-off-by: John Keeping <john@metanate.com>
---
v2:
- Set ep->need_prepare not ep->need_setup; this was missed when forward
  porting the patch as need_prepare is new in 6.1
- Add more details to the commit message about why it is safe to reset
  the interface here

 sound/usb/endpoint.c | 7 +++++++
 sound/usb/quirks.c   | 2 ++
 sound/usb/usbaudio.h | 4 ++++
 3 files changed, 13 insertions(+)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 310cd6fb0038..4aaf0784940b 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -1673,6 +1673,13 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, bool keep_pending)
 		stop_urbs(ep, false, keep_pending);
 		if (ep->clock_ref)
 			atomic_dec(&ep->clock_ref->locked);
+
+		if (ep->chip->quirk_flags & QUIRK_FLAG_FORCE_IFACE_RESET &&
+		    usb_pipeout(ep->pipe)) {
+			ep->need_prepare = true;
+			if (ep->iface_ref)
+				ep->iface_ref->need_setup = true;
+		}
 	}
 }
 
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 0f4dd3503a6a..58b37bfc885c 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -2044,6 +2044,8 @@ static const struct usb_audio_quirk_flags_table quirk_flags_table[] = {
 	DEVICE_FLG(0x0644, 0x804a, /* TEAC UD-301 */
 		   QUIRK_FLAG_ITF_USB_DSD_DAC | QUIRK_FLAG_CTL_MSG_DELAY |
 		   QUIRK_FLAG_IFACE_DELAY),
+	DEVICE_FLG(0x0644, 0x805f, /* TEAC Model 12 */
+		   QUIRK_FLAG_FORCE_IFACE_RESET),
 	DEVICE_FLG(0x06f8, 0xb000, /* Hercules DJ Console (Windows Edition) */
 		   QUIRK_FLAG_IGNORE_CTL_ERROR),
 	DEVICE_FLG(0x06f8, 0xd002, /* Hercules DJ Console (Macintosh Edition) */
diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index e97141ef730a..2aba508a4831 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -172,6 +172,9 @@ extern bool snd_usb_skip_validation;
  *  Don't apply implicit feedback sync mode
  * QUIRK_FLAG_IFACE_SKIP_CLOSE
  *  Don't closed interface during setting sample rate
+ * QUIRK_FLAG_FORCE_IFACE_RESET
+ *  Force an interface reset whenever stopping & restarting a stream
+ *  (e.g. after xrun)
  */
 
 #define QUIRK_FLAG_GET_SAMPLE_RATE	(1U << 0)
@@ -194,5 +197,6 @@ extern bool snd_usb_skip_validation;
 #define QUIRK_FLAG_GENERIC_IMPLICIT_FB	(1U << 17)
 #define QUIRK_FLAG_SKIP_IMPLICIT_FB	(1U << 18)
 #define QUIRK_FLAG_IFACE_SKIP_CLOSE	(1U << 19)
+#define QUIRK_FLAG_FORCE_IFACE_RESET	(1U << 20)
 
 #endif /* __USBAUDIO_H */
-- 
2.38.1