[PATCH 5/6] ALSA: usb-audio: Add PM guards to RME Digiface controls

[Will Porter]

The RME Digiface status and register helpers issue vendor requests
without preventing runtime suspend or disconnect. The volatile status
controls can repeatedly reach these unguarded paths while userspace
polls them.

Protect both helpers with snd_usb_lock. All Digiface get and put
callbacks then resume the device and hold the disconnect reference
across their transfer.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Will Porter <mrwillporter@xxxxxxxxx>
---
 sound/usb/mixer_quirks.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index a1f5592cc5d5..fc622eb95dc5 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -3480,6 +3480,10 @@ static int snd_rme_digiface_write_reg(struct snd_kcontrol *kcontrol, int item, u
 	struct usb_device *dev = chip->dev;
 	int err;
 
+	CLASS(snd_usb_lock, pm)(chip);
+	if (pm.err < 0)
+		return -EIO;
+
 	err = snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0),
 			      item,
 			      USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
@@ -3499,6 +3503,10 @@ static int snd_rme_digiface_read_status(struct snd_kcontrol *kcontrol, u32 statu
 	__le32 buf[4] = {};
 	int err;
 
+	CLASS(snd_usb_lock, pm)(chip);
+	if (pm.err < 0)
+		return -EIO;
+
 	err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0),
 			      RME_DIGIFACE_READ_STATUS,
 			      USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
-- 
2.47.3