[PATCH 2/6] ALSA: usb-audio: Add PM guards to US-16x08 transfers

[Will Porter <mrwillporter@gmail.com>]

The TASCAM control helpers submit vendor requests without preventing
runtime suspend or disconnect. This affects mixer writes and the
volatile meter path.

Protect both send and receive helpers with snd_usb_lock. Acquire the PM
guard before chip->mutex in the receive path so autoresume cannot invert
the mutex order.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Will Porter <mrwillporter@gmail.com>
---
 sound/usb/mixer_us16x08.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/usb/mixer_us16x08.c b/sound/usb/mixer_us16x08.c
index ebff185cbd2c..14fb1ad764a7 100644
--- a/sound/usb/mixer_us16x08.c
+++ b/sound/usb/mixer_us16x08.c
@@ -151,6 +151,9 @@ static const char *const route_names[] = {
 static int snd_us16x08_recv_urb(struct snd_usb_audio *chip,
 	unsigned char *buf, int size)
 {
+	CLASS(snd_usb_lock, pm)(chip);
+	if (pm.err < 0)
+		return -EIO;
 
 	guard(mutex)(&chip->mutex);
 	snd_usb_ctl_msg(chip->dev,
@@ -165,6 +168,10 @@ static int snd_us16x08_recv_urb(struct snd_usb_audio *chip,
  */
 static int snd_us16x08_send_urb(struct snd_usb_audio *chip, char *buf, int size)
 {
+	CLASS(snd_usb_lock, pm)(chip);
+	if (pm.err < 0)
+		return -EIO;
+
 	return snd_usb_ctl_msg(chip->dev, usb_sndctrlpipe(chip->dev, 0),
 			SND_US16X08_URB_REQUEST, SND_US16X08_URB_REQUESTTYPE,
 			0, 0, buf, size);
-- 
2.47.3