[PATCH] ALSA: caiaq: Fix control_put() result and cache rollback

[PATCH] ALSA: caiaq: Fix control_put() result and cache rollback

[Cássio Gabriel]

control_put() always returns 1 and updates cdev->control_state[]
before sending the USB command. It also ignores transport errors
from usb_bulk_msg(), snd_usb_caiaq_send_command(), and
snd_usb_caiaq_send_command_bank().

That breaks the ALSA .put() contract and can leave control_get()
reporting a cached value the device never accepted.

Return 0 for unchanged values, propagate transport failures,
and restore the cached byte when the write fails.

Fixes: 8e3cd08ed8e59 ("[ALSA] caiaq - add control API and more input features")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
---
 sound/usb/caiaq/control.c | 52 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 16 deletions(-)

diff --git a/sound/usb/caiaq/control.c b/sound/usb/caiaq/control.c
index af459c49baf4..4598fb7e8be0 100644
--- a/sound/usb/caiaq/control.c
+++ b/sound/usb/caiaq/control.c
@@ -87,6 +87,7 @@ static int control_put(struct snd_kcontrol *kcontrol,
 	struct snd_usb_caiaqdev *cdev = caiaqdev(chip->card);
 	int pos = kcontrol->private_value;
 	int v = ucontrol->value.integer.value[0];
+	int ret;
 	unsigned char cmd;
 
 	switch (cdev->chip.usb_id) {
@@ -103,6 +104,10 @@ static int control_put(struct snd_kcontrol *kcontrol,
 
 	if (pos & CNT_INTVAL) {
 		int i = pos & ~CNT_INTVAL;
+		unsigned char old = cdev->control_state[i];
+
+		if (old == v)
+			return 0;
 
 		cdev->control_state[i] = v;
 
@@ -113,10 +118,11 @@ static int control_put(struct snd_kcontrol *kcontrol,
 			cdev->ep8_out_buf[0] = i;
 			cdev->ep8_out_buf[1] = v;
 
-			usb_bulk_msg(cdev->chip.dev,
-				     usb_sndbulkpipe(cdev->chip.dev, 8),
-				     cdev->ep8_out_buf, sizeof(cdev->ep8_out_buf),
-				     &actual_len, 200);
+			ret = usb_bulk_msg(cdev->chip.dev,
+					   usb_sndbulkpipe(cdev->chip.dev, 8),
+					   cdev->ep8_out_buf,
+					   sizeof(cdev->ep8_out_buf),
+					   &actual_len, 200);
 		} else if (cdev->chip.usb_id ==
 			USB_ID(USB_VID_NATIVEINSTRUMENTS, USB_PID_MASCHINECONTROLLER)) {
 
@@ -128,21 +134,36 @@ static int control_put(struct snd_kcontrol *kcontrol,
 				offset = MASCHINE_BANK_SIZE;
 			}
 
-			snd_usb_caiaq_send_command_bank(cdev, cmd, bank,
-					cdev->control_state + offset,
-					MASCHINE_BANK_SIZE);
+			ret = snd_usb_caiaq_send_command_bank(cdev, cmd, bank,
+							      cdev->control_state + offset,
+							      MASCHINE_BANK_SIZE);
 		} else {
-			snd_usb_caiaq_send_command(cdev, cmd,
-					cdev->control_state, sizeof(cdev->control_state));
+			ret = snd_usb_caiaq_send_command(cdev, cmd,
+							 cdev->control_state,
+							 sizeof(cdev->control_state));
+		}
+
+		if (ret < 0) {
+			cdev->control_state[i] = old;
+			return ret;
 		}
 	} else {
-		if (v)
-			cdev->control_state[pos / 8] |= 1 << (pos % 8);
-		else
-			cdev->control_state[pos / 8] &= ~(1 << (pos % 8));
+		int idx = pos / 8;
+		unsigned char mask = 1 << (pos % 8);
+		unsigned char old = cdev->control_state[idx];
+		unsigned char val = v ? (old | mask) : (old & ~mask);
 
-		snd_usb_caiaq_send_command(cdev, cmd,
-				cdev->control_state, sizeof(cdev->control_state));
+		if (old == val)
+			return 0;
+
+		cdev->control_state[idx] = val;
+		ret = snd_usb_caiaq_send_command(cdev, cmd,
+						 cdev->control_state,
+						 sizeof(cdev->control_state));
+		if (ret < 0) {
+			cdev->control_state[idx] = old;
+			return ret;
+		}
 	}
 
 	return 1;
@@ -640,4 +661,3 @@ int snd_usb_caiaq_control_init(struct snd_usb_caiaqdev *cdev)
 
 	return ret;
 }
-

---
base-commit: c4643e7c7f45a07f26e01a4a617b859c01dabb3d
change-id: 20260416-caiaq-control-put-50be8a70431d

Best regards,
--  
Cássio Gabriel <cassiogabrielcontato@gmail.com>

Re: [PATCH] ALSA: caiaq: Fix control_put() result and cache rollback

[Takashi Iwai]

On Fri, 17 Apr 2026 15:41:33 +0200,
Cássio Gabriel wrote:
> 
> control_put() always returns 1 and updates cdev->control_state[]
> before sending the USB command. It also ignores transport errors
> from usb_bulk_msg(), snd_usb_caiaq_send_command(), and
> snd_usb_caiaq_send_command_bank().
> 
> That breaks the ALSA .put() contract and can leave control_get()
> reporting a cached value the device never accepted.
> 
> Return 0 for unchanged values, propagate transport failures,
> and restore the cached byte when the write fails.
> 
> Fixes: 8e3cd08ed8e59 ("[ALSA] caiaq - add control API and more input features")
> Cc: stable@vger.kernel.org
> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>

Applied now.  Thanks.


Takashi