[PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Zipdox]

Hello,

The USB Audio Mixer Unit driver (sound/usb/mixer.c) sends audio class
1.0 format control messages to devices, regardless of the actual audio
class version. This means audio class 2.0 devices will receive incorrect
messages, stall, and cause the driver to error (e.g. alsamixer exits
with a broken pipe error). This patch implements the GET_CUR, SET_CUR,
and RANGE control requests for mixer units according to the Audio Class
2.0 specification.

I have one question though, which has to do with the get_cur_mix_raw
function. It states "channel = 0: master, 1 = first channel", but as far
as I know the spec doesn't specify a master control for mixer units. I
implemented it so that channel 0 results the channel 1 value, but maybe
some other solution is desirable.

From: Zipdox <zipdox@zipdox.net>
Date: Tue, 15 Sep 2026 10:12:01 +0200
Subject: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and
  RANGE

Signed-off-by: Zipdox <zipdox@zipdox.net>
---
  sound/usb/mixer.c | 191 ++++++++++++++++++++++++++++++++--------------
  1 file changed, 133 insertions(+), 58 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ecaa8bc08d7c..99270731d409 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -360,12 +360,12 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
  	{
  		CLASS(snd_usb_lock, pm)(chip);
  		if (pm.err)
-			return -EIO;
+		return -EIO;
  
-		idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
-		ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), bRequest,
-				      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
-				      validx, idx, buf, size);
+	idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
+	ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), bRequest,
+			      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
+			      validx, idx, buf, size);
  	}
  
  	if (ret < 0) {
@@ -410,6 +410,53 @@ static int get_ctl_value(struct usb_mixer_elem_info *cval, int request,
  		get_ctl_value_v2(cval, request, validx, value_ret);
  }
  
+static int get_ctl_range_16(struct usb_mixer_elem_info *cval)
+{
+	struct snd_usb_audio *chip = cval->head.mixer->chip;
+	int idx;
+	int ret;
+	__u16 wNumSubRanges;
+	__u8 range_res[8] = {0};
+
+	__u8 mcn = (cval->control - 1) * cval->channels;
+	__u16 wValue = (UAC2_MU_MIXER << 8) | mcn;
+
+	if (snd_usb_lock_shutdown(chip))
+		return -EIO;
+
+	idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
+	ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), UAC2_CS_RANGE,
+			      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
+			      wValue, idx, range_res, sizeof(range_res));
+	snd_usb_unlock_shutdown(chip);
+
+	if (ret < 0) {
+		usb_audio_dbg(chip,
+			"cannot get ctl range: req = %#x, wValue = %#x, wIndex = %#x\n",
+			UAC2_CS_RANGE, wValue, idx);
+		return ret;
+	}
+
+	wNumSubRanges = combine_word(&range_res[0]);
+	if(wNumSubRanges != 1) {
+		usb_audio_dbg(chip,
+			"unexpected wNumSubRanges (%u) for ctl range: req = %#x, wValue = %#x, wIndex = %#x\n",
+			(unsigned int)wNumSubRanges, UAC2_CS_RANGE, wValue, idx);
+		return -EIO;
+	}
+
+	cval->min = combine_word(&range_res[2]);
+	if (cval->min >= 0x8000) cval->min -= 0x10000;
+	cval->max = combine_word(&range_res[4]);
+	if (cval->max >= 0x8000) cval->max -= 0x10000;
+	cval->res = combine_word(&range_res[6]);
+	usb_audio_dbg(chip,
+		"range for mcn = %u: min = %d, max = %d, res = %d\n",
+		(unsigned int)mcn, cval->min, cval->max, cval->res);
+
+	return 0;
+}
+
  static int get_cur_ctl_value(struct usb_mixer_elem_info *cval,
  			     int validx, int *value)
  {
@@ -420,9 +467,18 @@ static int get_cur_ctl_value(struct usb_mixer_elem_info *cval,
  static inline int get_cur_mix_raw(struct usb_mixer_elem_info *cval,
  				  int channel, int *value)
  {
-	return get_ctl_value(cval, UAC_GET_CUR,
+	if(cval->head.mixer->protocol == UAC_VERSION_1){
+		return get_ctl_value(cval, UAC_GET_CUR,
  			     (cval->control << 8) | channel,
  			     value);
+	}else{
+		__u8 mcn = (cval->control - 1) * cval->channels + ((channel == 0 ? 1 : channel) - 1);
+		__u16 wValue = (UAC2_MU_MIXER << 8) | mcn;
+		return get_ctl_value(cval, UAC_GET_CUR,
+			     wValue,
+			     value);
+	}
+	
  }
  
  int snd_usb_get_cur_mix_value(struct usb_mixer_elem_info *cval,
@@ -527,9 +583,18 @@ int snd_usb_set_cur_mix_value(struct usb_mixer_elem_info *cval, int channel,
  		return 0;
  	}
  
-	err = snd_usb_mixer_set_ctl_value(cval,
-					  UAC_SET_CUR, (cval->control << 8) | channel,
-					  value);
+	if(cval->head.mixer->protocol == UAC_VERSION_1){
+		err = snd_usb_mixer_set_ctl_value(cval,
+						UAC_SET_CUR, (cval->control << 8) | channel,
+						value);
+	}else{
+		__u8 mcn = (cval->control - 1) * cval->channels + ((channel == 0 ? 1 : channel) - 1);
+		__u16 wValue = (UAC2_MU_MIXER << 8) | mcn;
+		err = snd_usb_mixer_set_ctl_value(cval,
+						UAC_SET_CUR, wValue,
+						value);
+	}
+
  	if (err < 0)
  		return err;
  	cval->cached |= BIT(channel);
@@ -1336,59 +1401,69 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
  	    cval->val_type == USB_MIXER_INV_BOOLEAN) {
  		cval->initialized = 1;
  	} else {
-		int minchn = 0;
-		if (cval->cmask) {
-			for (i = 0; i < MAX_CHANNELS; i++)
-				if (cval->cmask & BIT(i)) {
-					minchn = i + 1;
-					break;
-				}
-		}
-		if (get_ctl_value(cval, UAC_GET_MAX, (cval->control << 8) | minchn, &cval->max) < 0 ||
-		    get_ctl_value(cval, UAC_GET_MIN, (cval->control << 8) | minchn, &cval->min) < 0) {
-			usb_audio_err(cval->head.mixer->chip,
-				      "%d:%d: cannot get min/max values for control %d (id %d)\n",
-				   cval->head.id, mixer_ctrl_intf(cval->head.mixer),
-							       cval->control, cval->head.id);
-			return -EAGAIN;
-		}
-		if (get_ctl_value(cval, UAC_GET_RES,
-				  (cval->control << 8) | minchn,
-				  &cval->res) < 0) {
-			cval->res = 1;
-		} else if (cval->head.mixer->protocol == UAC_VERSION_1) {
-			int last_valid_res = cval->res;
-
-			while (cval->res > 1) {
-				if (snd_usb_mixer_set_ctl_value(cval, UAC_SET_RES,
-								(cval->control << 8) | minchn,
-								cval->res / 2) < 0)
-					break;
-				cval->res /= 2;
+		if(cval->head.mixer->protocol == UAC_VERSION_1){
+			int minchn = 0;
+			if (cval->cmask) {
+				for (i = 0; i < MAX_CHANNELS; i++)
+					if (cval->cmask & BIT(i)) {
+						minchn = i + 1;
+						break;
+					}
+			}
+			if (get_ctl_value(cval, UAC_GET_MAX, (cval->control << 8) | minchn, &cval->max) < 0 ||
+				get_ctl_value(cval, UAC_GET_MIN, (cval->control << 8) | minchn, &cval->min) < 0) {
+				usb_audio_err(cval->head.mixer->chip,
+						"%d:%d: cannot get min/max values for control %d (id %d)\n",
+					cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+									cval->control, cval->head.id);
+				return -EAGAIN;
  			}
  			if (get_ctl_value(cval, UAC_GET_RES,
-					  (cval->control << 8) | minchn, &cval->res) < 0)
-				cval->res = last_valid_res;
-		}
-		if (cval->res == 0)
-			cval->res = 1;
+					(cval->control << 8) | minchn,
+					&cval->res) < 0) {
+				cval->res = 1;
+			} else if (cval->head.mixer->protocol == UAC_VERSION_1) {
+				int last_valid_res = cval->res;
+
+				while (cval->res > 1) {
+					if (snd_usb_mixer_set_ctl_value(cval, UAC_SET_RES,
+									(cval->control << 8) | minchn,
+									cval->res / 2) < 0)
+						break;
+					cval->res /= 2;
+				}
+				if (get_ctl_value(cval, UAC_GET_RES,
+						(cval->control << 8) | minchn, &cval->res) < 0)
+					cval->res = last_valid_res;
+			}
+			if (cval->res == 0)
+				cval->res = 1;
  
-		if (cval->min < cval->max) {
-			int saved;
+			if (cval->min < cval->max) {
+				int saved;
  
-			if (get_cur_mix_raw(cval, minchn, &saved) < 0)
-				goto no_checks;
+				if (get_cur_mix_raw(cval, minchn, &saved) < 0)
+					goto no_checks;
  
-			ret = check_sticky_volume_control(cval, minchn, saved);
-			if (ret)
-				goto no_checks;
+				ret = check_sticky_volume_control(cval, minchn, saved);
+				if (ret)
+					goto no_checks;
  
-			if (cval->min + cval->res < cval->max)
-				check_volume_control_res(cval, minchn, saved);
+				if (cval->min + cval->res < cval->max)
+					check_volume_control_res(cval, minchn, saved);
  
-			snd_usb_set_cur_mix_value(cval, minchn, 0, saved);
-		}
+				snd_usb_set_cur_mix_value(cval, minchn, 0, saved);
+			}
  
+		}else{
+			if(get_ctl_range_16(cval) < 0){
+				usb_audio_err(cval->head.mixer->chip,
+				"%d:%d: cannot get min/max values for control %d (id %d)\n",
+					cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+									cval->control, cval->head.id);
+				return -EINVAL;
+			}
+		}
  no_checks:
  		/*
  		 * Got a non-fatal failure during sanity checks.
@@ -1983,9 +2058,9 @@ static void __build_feature_ctl(struct usb_mixer_interface *mixer,
  			       cval->head.id, kctl->id.name, cval->channels,
  			       cval->min, cval->max, cval->res);
  	} else {
-		usb_audio_dbg(mixer->chip, "[%d] FU [%s] ch = %d, val = %d/%d/%d\n",
-			      cval->head.id, kctl->id.name, cval->channels,
-			      cval->min, cval->max, cval->res);
+	usb_audio_dbg(mixer->chip, "[%d] FU [%s] ch = %d, val = %d/%d/%d\n",
+		      cval->head.id, kctl->id.name, cval->channels,
+		      cval->min, cval->max, cval->res);
  	}
  
  	snd_usb_mixer_add_control(&cval->head, kctl);
@@ -3550,7 +3625,7 @@ void snd_usb_mixer_notify_id(struct usb_mixer_interface *mixer, int unitid)
  		info = mixer_elem_list_to_info(list);
  		/* invalidate cache, so the value is read from the device */
  		if (!info->get_cur_broken)
-			info->cached = 0;
+		info->cached = 0;
  		snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_VALUE,
  			       &list->kctl->id);
  	}
-- 
2.47.3

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Takashi Iwai]

On Tue, 15 Sep 2026 10:54:00 +0200,
Zipdox wrote:
> 
> Hello,
> 
> The USB Audio Mixer Unit driver (sound/usb/mixer.c) sends audio class
> 1.0 format control messages to devices, regardless of the actual audio
> class version. This means audio class 2.0 devices will receive incorrect
> messages, stall, and cause the driver to error (e.g. alsamixer exits
> with a broken pipe error).

Hmm, for UAC2, UAC_GET_CUR & co isn't passed as is at all, but the
call is translated to UAC2_CS_CUR and UAC2_CS_RANGE accordingly in
get_ctl_value_v2() (that is called from get_ctl_value()
conditionally).  So this translation path was skipped somehow with
your device...?


> This patch implements the GET_CUR, SET_CUR,
> and RANGE control requests for mixer units according to the Audio Class
> 2.0 specification.
> 
> I have one question though, which has to do with the get_cur_mix_raw
> function. It states "channel = 0: master, 1 = first channel", but as far
> as I know the spec doesn't specify a master control for mixer units. I
> implemented it so that channel 0 results the channel 1 value, but maybe
> some other solution is desirable.
> 
> From: Zipdox <zipdox@zipdox.net>
> Date: Tue, 15 Sep 2026 10:12:01 +0200
> Subject: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and
>  RANGE
> 
> Signed-off-by: Zipdox <zipdox@zipdox.net>

Could you try to reformat in a proper patch format?
Also, it looks containing many unnecessary / unrelated changes that
make review more difficult.  Please try to concentrate only on the
change you really need.


thanks,

Takashi

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Zipdox]

On 9/15/26 1:08 PM, Takashi Iwai wrote:
> Hmm, for UAC2, UAC_GET_CUR & co isn't passed as is at all, but the
> call is translated to UAC2_CS_CUR and UAC2_CS_RANGE accordingly in
> get_ctl_value_v2() (that is called from get_ctl_value()
> conditionally).  So this translation path was skipped somehow with
> your device...?

The request is translated yes, but wValue is incorrect. UAC2 uses a
Mixer Control Number ("mcn") in the low byte to identify the mixer
control, along with a control selector in the high byte (UAC2_MU_MIXER
in this case). UAC1 on the other hand uses the low and high byte to
identify the mixer control. It seems get_ctl_value_v2 doesn't change
wValue to the appropriate format (mcn and control selector). This code
was, as far as I understand it, never correct to begin with for UAC2.

To get the MIN, MAX, and RES, get_min_max_with_quirks currently calls
get_ctl_value three times to get the values separately. It looks like
get_ctl_value_v2 was written to send RANGE requests and extract the
appropriate part of the RANGE response, depending on the request. This
doesn't actually work though, because wValue is incorrect as I stated
above. It also unnecessarily sends three requests instead of one. That's
why I bypassed it entirely and wrote the get_ctl_range_16 function. This
could in theory be consolidated, but there's quite a bit of other code
so I'm hesitant to touch it. Supplying the correct wValue to
get_ctl_value in get_cur_mix_raw fixed getting the current value, and
the same applies to the call to snd_usb_mixer_set_ctl_value in
snd_usb_set_cur_mix_value.

> Could you try to reformat in a proper patch format?
> Also, it looks containing many unnecessary / unrelated changes that
> make review more difficult.  Please try to concentrate only on the
> change you really need.

Perhaps you are referring to the indentation changes resulting from
wrapping existing code in an if statement? I can't really do anything
about that. I don't think I changed any unrelated code itself. If there
are unrelated changes, please point them out to me. In any case, I
changed the patch to the "canonical patch format" as written in the
kernel docs.

From: Zipdox <zipdox@zipdox.net>

The USB Audio Mixer Unit driver (sound/usb/mixer.c) sends audio class
1.0 format control messages to devices, regardless of the actual audio
class version. This means audio class 2.0 devices will receive incorrect
messages, stall, and cause the driver to error (e.g. alsamixer exits
with a broken pipe error). This patch implements the GET_CUR, SET_CUR,
and RANGE control requests for mixer units according to the Audio Class
2.0 specification.

Subject: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

Signed-off-by: Zipdox <zipdox@zipdox.net>
---
  sound/usb/mixer.c | 191 ++++++++++++++++++++++++++++++++--------------
  1 file changed, 133 insertions(+), 58 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ecaa8bc08d7c..99270731d409 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -360,12 +360,12 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
  	{
  		CLASS(snd_usb_lock, pm)(chip);
  		if (pm.err)
-			return -EIO;
+		return -EIO;
  
-		idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
-		ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), bRequest,
-				      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
-				      validx, idx, buf, size);
+	idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
+	ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), bRequest,
+			      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
+			      validx, idx, buf, size);
  	}
  
  	if (ret < 0) {
@@ -410,6 +410,53 @@ static int get_ctl_value(struct usb_mixer_elem_info *cval, int request,
  		get_ctl_value_v2(cval, request, validx, value_ret);
  }
  
+static int get_ctl_range_16(struct usb_mixer_elem_info *cval)
+{
+	struct snd_usb_audio *chip = cval->head.mixer->chip;
+	int idx;
+	int ret;
+	__u16 wNumSubRanges;
+	__u8 range_res[8] = {0};
+
+	__u8 mcn = (cval->control - 1) * cval->channels;
+	__u16 wValue = (UAC2_MU_MIXER << 8) | mcn;
+
+	if (snd_usb_lock_shutdown(chip))
+		return -EIO;
+
+	idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
+	ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), UAC2_CS_RANGE,
+			      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
+			      wValue, idx, range_res, sizeof(range_res));
+	snd_usb_unlock_shutdown(chip);
+
+	if (ret < 0) {
+		usb_audio_dbg(chip,
+			"cannot get ctl range: req = %#x, wValue = %#x, wIndex = %#x\n",
+			UAC2_CS_RANGE, wValue, idx);
+		return ret;
+	}
+
+	wNumSubRanges = combine_word(&range_res[0]);
+	if(wNumSubRanges != 1) {
+		usb_audio_dbg(chip,
+			"unexpected wNumSubRanges (%u) for ctl range: req = %#x, wValue = %#x, wIndex = %#x\n",
+			(unsigned int)wNumSubRanges, UAC2_CS_RANGE, wValue, idx);
+		return -EIO;
+	}
+
+	cval->min = combine_word(&range_res[2]);
+	if (cval->min >= 0x8000) cval->min -= 0x10000;
+	cval->max = combine_word(&range_res[4]);
+	if (cval->max >= 0x8000) cval->max -= 0x10000;
+	cval->res = combine_word(&range_res[6]);
+	usb_audio_dbg(chip,
+		"range for mcn = %u: min = %d, max = %d, res = %d\n",
+		(unsigned int)mcn, cval->min, cval->max, cval->res);
+
+	return 0;
+}
+
  static int get_cur_ctl_value(struct usb_mixer_elem_info *cval,
  			     int validx, int *value)
  {
@@ -420,9 +467,18 @@ static int get_cur_ctl_value(struct usb_mixer_elem_info *cval,
  static inline int get_cur_mix_raw(struct usb_mixer_elem_info *cval,
  				  int channel, int *value)
  {
-	return get_ctl_value(cval, UAC_GET_CUR,
+	if(cval->head.mixer->protocol == UAC_VERSION_1){
+		return get_ctl_value(cval, UAC_GET_CUR,
  			     (cval->control << 8) | channel,
  			     value);
+	}else{
+		__u8 mcn = (cval->control - 1) * cval->channels + ((channel == 0 ? 1 : channel) - 1);
+		__u16 wValue = (UAC2_MU_MIXER << 8) | mcn;
+		return get_ctl_value(cval, UAC_GET_CUR,
+			     wValue,
+			     value);
+	}
+	
  }
  
  int snd_usb_get_cur_mix_value(struct usb_mixer_elem_info *cval,
@@ -527,9 +583,18 @@ int snd_usb_set_cur_mix_value(struct usb_mixer_elem_info *cval, int channel,
  		return 0;
  	}
  
-	err = snd_usb_mixer_set_ctl_value(cval,
-					  UAC_SET_CUR, (cval->control << 8) | channel,
-					  value);
+	if(cval->head.mixer->protocol == UAC_VERSION_1){
+		err = snd_usb_mixer_set_ctl_value(cval,
+						UAC_SET_CUR, (cval->control << 8) | channel,
+						value);
+	}else{
+		__u8 mcn = (cval->control - 1) * cval->channels + ((channel == 0 ? 1 : channel) - 1);
+		__u16 wValue = (UAC2_MU_MIXER << 8) | mcn;
+		err = snd_usb_mixer_set_ctl_value(cval,
+						UAC_SET_CUR, wValue,
+						value);
+	}
+
  	if (err < 0)
  		return err;
  	cval->cached |= BIT(channel);
@@ -1336,59 +1401,69 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
  	    cval->val_type == USB_MIXER_INV_BOOLEAN) {
  		cval->initialized = 1;
  	} else {
-		int minchn = 0;
-		if (cval->cmask) {
-			for (i = 0; i < MAX_CHANNELS; i++)
-				if (cval->cmask & BIT(i)) {
-					minchn = i + 1;
-					break;
-				}
-		}
-		if (get_ctl_value(cval, UAC_GET_MAX, (cval->control << 8) | minchn, &cval->max) < 0 ||
-		    get_ctl_value(cval, UAC_GET_MIN, (cval->control << 8) | minchn, &cval->min) < 0) {
-			usb_audio_err(cval->head.mixer->chip,
-				      "%d:%d: cannot get min/max values for control %d (id %d)\n",
-				   cval->head.id, mixer_ctrl_intf(cval->head.mixer),
-							       cval->control, cval->head.id);
-			return -EAGAIN;
-		}
-		if (get_ctl_value(cval, UAC_GET_RES,
-				  (cval->control << 8) | minchn,
-				  &cval->res) < 0) {
-			cval->res = 1;
-		} else if (cval->head.mixer->protocol == UAC_VERSION_1) {
-			int last_valid_res = cval->res;
-
-			while (cval->res > 1) {
-				if (snd_usb_mixer_set_ctl_value(cval, UAC_SET_RES,
-								(cval->control << 8) | minchn,
-								cval->res / 2) < 0)
-					break;
-				cval->res /= 2;
+		if(cval->head.mixer->protocol == UAC_VERSION_1){
+			int minchn = 0;
+			if (cval->cmask) {
+				for (i = 0; i < MAX_CHANNELS; i++)
+					if (cval->cmask & BIT(i)) {
+						minchn = i + 1;
+						break;
+					}
+			}
+			if (get_ctl_value(cval, UAC_GET_MAX, (cval->control << 8) | minchn, &cval->max) < 0 ||
+				get_ctl_value(cval, UAC_GET_MIN, (cval->control << 8) | minchn, &cval->min) < 0) {
+				usb_audio_err(cval->head.mixer->chip,
+						"%d:%d: cannot get min/max values for control %d (id %d)\n",
+					cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+									cval->control, cval->head.id);
+				return -EAGAIN;
  			}
  			if (get_ctl_value(cval, UAC_GET_RES,
-					  (cval->control << 8) | minchn, &cval->res) < 0)
-				cval->res = last_valid_res;
-		}
-		if (cval->res == 0)
-			cval->res = 1;
+					(cval->control << 8) | minchn,
+					&cval->res) < 0) {
+				cval->res = 1;
+			} else if (cval->head.mixer->protocol == UAC_VERSION_1) {
+				int last_valid_res = cval->res;
+
+				while (cval->res > 1) {
+					if (snd_usb_mixer_set_ctl_value(cval, UAC_SET_RES,
+									(cval->control << 8) | minchn,
+									cval->res / 2) < 0)
+						break;
+					cval->res /= 2;
+				}
+				if (get_ctl_value(cval, UAC_GET_RES,
+						(cval->control << 8) | minchn, &cval->res) < 0)
+					cval->res = last_valid_res;
+			}
+			if (cval->res == 0)
+				cval->res = 1;
  
-		if (cval->min < cval->max) {
-			int saved;
+			if (cval->min < cval->max) {
+				int saved;
  
-			if (get_cur_mix_raw(cval, minchn, &saved) < 0)
-				goto no_checks;
+				if (get_cur_mix_raw(cval, minchn, &saved) < 0)
+					goto no_checks;
  
-			ret = check_sticky_volume_control(cval, minchn, saved);
-			if (ret)
-				goto no_checks;
+				ret = check_sticky_volume_control(cval, minchn, saved);
+				if (ret)
+					goto no_checks;
  
-			if (cval->min + cval->res < cval->max)
-				check_volume_control_res(cval, minchn, saved);
+				if (cval->min + cval->res < cval->max)
+					check_volume_control_res(cval, minchn, saved);
  
-			snd_usb_set_cur_mix_value(cval, minchn, 0, saved);
-		}
+				snd_usb_set_cur_mix_value(cval, minchn, 0, saved);
+			}
  
+		}else{
+			if(get_ctl_range_16(cval) < 0){
+				usb_audio_err(cval->head.mixer->chip,
+				"%d:%d: cannot get min/max values for control %d (id %d)\n",
+					cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+									cval->control, cval->head.id);
+				return -EINVAL;
+			}
+		}
  no_checks:
  		/*
  		 * Got a non-fatal failure during sanity checks.
@@ -1983,9 +2058,9 @@ static void __build_feature_ctl(struct usb_mixer_interface *mixer,
  			       cval->head.id, kctl->id.name, cval->channels,
  			       cval->min, cval->max, cval->res);
  	} else {
-		usb_audio_dbg(mixer->chip, "[%d] FU [%s] ch = %d, val = %d/%d/%d\n",
-			      cval->head.id, kctl->id.name, cval->channels,
-			      cval->min, cval->max, cval->res);
+	usb_audio_dbg(mixer->chip, "[%d] FU [%s] ch = %d, val = %d/%d/%d\n",
+		      cval->head.id, kctl->id.name, cval->channels,
+		      cval->min, cval->max, cval->res);
  	}
  
  	snd_usb_mixer_add_control(&cval->head, kctl);
@@ -3550,7 +3625,7 @@ void snd_usb_mixer_notify_id(struct usb_mixer_interface *mixer, int unitid)
  		info = mixer_elem_list_to_info(list);
  		/* invalidate cache, so the value is read from the device */
  		if (!info->get_cur_broken)
-			info->cached = 0;
+		info->cached = 0;
  		snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_VALUE,
  			       &list->kctl->id);
  	}
-- 
2.47.3

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Takashi Iwai]

On Tue, 15 Sep 2026 14:54:38 +0200,
Zipdox wrote:
> 
> On 9/15/26 1:08 PM, Takashi Iwai wrote:
> > Hmm, for UAC2, UAC_GET_CUR & co isn't passed as is at all, but the
> > call is translated to UAC2_CS_CUR and UAC2_CS_RANGE accordingly in
> > get_ctl_value_v2() (that is called from get_ctl_value()
> > conditionally).  So this translation path was skipped somehow with
> > your device...?
> 
> The request is translated yes, but wValue is incorrect. UAC2 uses a
> Mixer Control Number ("mcn") in the low byte to identify the mixer
> control, along with a control selector in the high byte (UAC2_MU_MIXER
> in this case). UAC1 on the other hand uses the low and high byte to
> identify the mixer control. It seems get_ctl_value_v2 doesn't change
> wValue to the appropriate format (mcn and control selector). This code
> was, as far as I understand it, never correct to begin with for UAC2.

OK, point taken.

> To get the MIN, MAX, and RES, get_min_max_with_quirks currently calls
> get_ctl_value three times to get the values separately. It looks like
> get_ctl_value_v2 was written to send RANGE requests and extract the
> appropriate part of the RANGE response, depending on the request. This
> doesn't actually work though, because wValue is incorrect as I stated
> above. It also unnecessarily sends three requests instead of one. That's
> why I bypassed it entirely and wrote the get_ctl_range_16 function. This
> could in theory be consolidated, but there's quite a bit of other code
> so I'm hesitant to touch it. Supplying the correct wValue to
> get_ctl_value in get_cur_mix_raw fixed getting the current value, and
> the same applies to the call to snd_usb_mixer_set_ctl_value in
> snd_usb_set_cur_mix_value.

But your code also blindly assumes the MU_MIXER_CONTROL that doesn't
fit with other units like feature unit?  I guess we have to set the
proper Control Selector value depending on the unit type.

After all, this is about the correct setup of wValue.  Let's try to be
minimalistic at first -- just tweak wValue in get_ctl_value_v2() and
snd_usb_mixer_set_ctl_value() at first.  If this becomes too ugly, we
can think of redesigning.


> > Could you try to reformat in a proper patch format?
> > Also, it looks containing many unnecessary / unrelated changes that
> > make review more difficult.  Please try to concentrate only on the
> > change you really need.
> 
> Perhaps you are referring to the indentation changes resulting from
> wrapping existing code in an if statement? I can't really do anything
> about that. I don't think I changed any unrelated code itself. If there
> are unrelated changes, please point them out to me.

Well, get_ctl_value_v2() changes look all unrelated and just breaking
indentations.

> In any case, I
> changed the patch to the "canonical patch format" as written in the
> kernel docs.
> 
> From: Zipdox <zipdox@zipdox.net>
> 
> The USB Audio Mixer Unit driver (sound/usb/mixer.c) sends audio class
> 1.0 format control messages to devices, regardless of the actual audio
> class version. This means audio class 2.0 devices will receive incorrect
> messages, stall, and cause the driver to error (e.g. alsamixer exits
> with a broken pipe error). This patch implements the GET_CUR, SET_CUR,
> and RANGE control requests for mixer units according to the Audio Class
> 2.0 specification.
> 
> Subject: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

The subject line must be at the beginning right after From tag.


> Signed-off-by: Zipdox <zipdox@zipdox.net>

... and both From and Signed-off-by should be with a real name (or a
known identity).  It's a legal requirement.


thanks,

Takashi

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Zipdox]

On 9/15/26 4:19 PM, Takashi Iwai wrote:
> But your code also blindly assumes the MU_MIXER_CONTROL that doesn't
> fit with other units like feature unit?  I guess we have to set the
> proper Control Selector value depending on the unit type.
> 
> After all, this is about the correct setup of wValue.  Let's try to be
> minimalistic at first -- just tweak wValue in get_ctl_value_v2() and
> snd_usb_mixer_set_ctl_value() at first.  If this becomes too ugly, we
> can think of redesigning.
I assumed that mixer.c was just for the mixer unit, and I seem to have 
completely overlooked the fact that that it also controls feature units. 
I'm not sure how to proceed from here. Do you have any suggestions for 
how we can store the control selector in the usb_mixer_elem_info struct? 
The control field is presently used as the input channel number, so 
maybe we should add a separate field for the input channel? I think 
maybe it's better that someone else fixes this, I'm kind of out of my 
element here.

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Takashi Iwai]

On Wed, 16 Sep 2026 09:43:14 +0200,
Zipdox wrote:
> 
> On 9/15/26 4:19 PM, Takashi Iwai wrote:
> > But your code also blindly assumes the MU_MIXER_CONTROL that doesn't
> > fit with other units like feature unit?  I guess we have to set the
> > proper Control Selector value depending on the unit type.
> > 
> > After all, this is about the correct setup of wValue.  Let's try to be
> > minimalistic at first -- just tweak wValue in get_ctl_value_v2() and
> > snd_usb_mixer_set_ctl_value() at first.  If this becomes too ugly, we
> > can think of redesigning.
> I assumed that mixer.c was just for the mixer unit, and I seem to have
> completely overlooked the fact that that it also controls feature
> units. I'm not sure how to proceed from here. Do you have any
> suggestions for how we can store the control selector in the
> usb_mixer_elem_info struct? The control field is presently used as the
> input channel number, so maybe we should add a separate field for the
> input channel? I think maybe it's better that someone else fixes this,
> I'm kind of out of my element here.

I took a look back at the current code, and at least, the parse of
UAC2 mixer unit itself is OK -- it handles the bitmap properly.
The problem is the exceptional way to set up wValue for the mixer
unit, and I guess something like below could work.  It just stores the
part of wValue in an additional field, and use it for calculating the
correct wValue with MCN + UAC2_MU_MIXER in high byte.

Just compile tested, so not 100% sure whether it's correct.


thanks,

Takashi

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -347,6 +347,10 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 
 	val_size = uac2_ctl_value_size(cval->val_type);
 
+	/* correct wValue for UAC2 mixer control with MCN */
+	if (cval->v2_mixer)
+		validx = cval->v2_mixer | ((validx & 0xff) - 1);
+
 	if (request == UAC_GET_CUR) {
 		bRequest = UAC2_CS_CUR;
 		size = val_size;
@@ -2345,6 +2349,10 @@ static void build_mixer_unit_ctl(struct mixer_build *state,
 
 	snd_usb_mixer_elem_init_std(&cval->head, state->mixer, unitid);
 	cval->control = in_ch + 1; /* based on 1 */
+	/* MCN is calculated later with the input channel based on v2_mixer */
+	if (state->mixer->protocol == UAC_VERSION_2 ||
+	    state->mixer->protocol == UAC_VERSION_3)
+		cval->v2_mixer = (UAC2_MU_MIXER << 8) | (in_ch * num_outs);
 	cval->val_type = USB_MIXER_S16;
 	for (i = 0; i < num_outs; i++) {
 		__u8 *c = uac_mixer_unit_bmControls(desc, state->mixer->protocol);
diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 037b446d8b6f..650f30026177 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -97,6 +97,7 @@ struct usb_mixer_elem_info {
 	u8 initialized;
 	u8 min_mute;
 	u8 get_cur_broken;
+	u16 v2_mixer;
 	void *private_data;
 };
 

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Takashi Iwai]

On Wed, 16 Sep 2026 17:40:53 +0200,
Takashi Iwai wrote:
> 
> On Wed, 16 Sep 2026 09:43:14 +0200,
> Zipdox wrote:
> > 
> > On 9/15/26 4:19 PM, Takashi Iwai wrote:
> > > But your code also blindly assumes the MU_MIXER_CONTROL that doesn't
> > > fit with other units like feature unit?  I guess we have to set the
> > > proper Control Selector value depending on the unit type.
> > > 
> > > After all, this is about the correct setup of wValue.  Let's try to be
> > > minimalistic at first -- just tweak wValue in get_ctl_value_v2() and
> > > snd_usb_mixer_set_ctl_value() at first.  If this becomes too ugly, we
> > > can think of redesigning.
> > I assumed that mixer.c was just for the mixer unit, and I seem to have
> > completely overlooked the fact that that it also controls feature
> > units. I'm not sure how to proceed from here. Do you have any
> > suggestions for how we can store the control selector in the
> > usb_mixer_elem_info struct? The control field is presently used as the
> > input channel number, so maybe we should add a separate field for the
> > input channel? I think maybe it's better that someone else fixes this,
> > I'm kind of out of my element here.
> 
> I took a look back at the current code, and at least, the parse of
> UAC2 mixer unit itself is OK -- it handles the bitmap properly.
> The problem is the exceptional way to set up wValue for the mixer
> unit, and I guess something like below could work.  It just stores the
> part of wValue in an additional field, and use it for calculating the
> correct wValue with MCN + UAC2_MU_MIXER in high byte.
> 
> Just compile tested, so not 100% sure whether it's correct.

... and this version was obviously half-baked, forgotten the
counterpart.  A revised patch is below.


Takashi

-- 8< --
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 33a6a1281410..0977fc58d0b5 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -347,6 +347,10 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 
 	val_size = uac2_ctl_value_size(cval->val_type);
 
+	/* correct wValue for UAC2 mixer control with MCN */
+	if (cval->v2_mixer)
+		validx = cval->v2_mixer | ((validx & 0xff) - 1);
+
 	if (request == UAC_GET_CUR) {
 		bRequest = UAC2_CS_CUR;
 		size = val_size;
@@ -478,6 +482,10 @@ int snd_usb_mixer_set_ctl_value(struct usb_mixer_elem_info *cval,
 		}
 
 		request = UAC2_CS_CUR;
+
+		/* correct wValue for UAC2 mixer control with MCN */
+		if (cval->v2_mixer)
+			validx = cval->v2_mixer | ((validx & 0xff) - 1);
 	}
 
 	value_set = convert_bytes_value(cval, value_set);
@@ -2345,6 +2353,10 @@ static void build_mixer_unit_ctl(struct mixer_build *state,
 
 	snd_usb_mixer_elem_init_std(&cval->head, state->mixer, unitid);
 	cval->control = in_ch + 1; /* based on 1 */
+	/* MCN is calculated later with the input channel based on v2_mixer */
+	if (state->mixer->protocol == UAC_VERSION_2 ||
+	    state->mixer->protocol == UAC_VERSION_3)
+		cval->v2_mixer = (UAC2_MU_MIXER << 8) | (in_ch * num_outs);
 	cval->val_type = USB_MIXER_S16;
 	for (i = 0; i < num_outs; i++) {
 		__u8 *c = uac_mixer_unit_bmControls(desc, state->mixer->protocol);
diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 037b446d8b6f..650f30026177 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -97,6 +97,7 @@ struct usb_mixer_elem_info {
 	u8 initialized;
 	u8 min_mute;
 	u8 get_cur_broken;
+	u16 v2_mixer;
 	void *private_data;
 };
 

Re: [PATCH] USB Audio Class 2 Mixer unit support for GET_CUR, SET_CUR and RANGE

[Takashi Iwai]

On Wed, 16 Sep 2026 18:58:50 +0200,
Takashi Iwai wrote:
> 
> On Wed, 16 Sep 2026 17:40:53 +0200,
> Takashi Iwai wrote:
> > 
> > On Wed, 16 Sep 2026 09:43:14 +0200,
> > Zipdox wrote:
> > > 
> > > On 9/15/26 4:19 PM, Takashi Iwai wrote:
> > > > But your code also blindly assumes the MU_MIXER_CONTROL that doesn't
> > > > fit with other units like feature unit?  I guess we have to set the
> > > > proper Control Selector value depending on the unit type.
> > > > 
> > > > After all, this is about the correct setup of wValue.  Let's try to be
> > > > minimalistic at first -- just tweak wValue in get_ctl_value_v2() and
> > > > snd_usb_mixer_set_ctl_value() at first.  If this becomes too ugly, we
> > > > can think of redesigning.
> > > I assumed that mixer.c was just for the mixer unit, and I seem to have
> > > completely overlooked the fact that that it also controls feature
> > > units. I'm not sure how to proceed from here. Do you have any
> > > suggestions for how we can store the control selector in the
> > > usb_mixer_elem_info struct? The control field is presently used as the
> > > input channel number, so maybe we should add a separate field for the
> > > input channel? I think maybe it's better that someone else fixes this,
> > > I'm kind of out of my element here.
> > 
> > I took a look back at the current code, and at least, the parse of
> > UAC2 mixer unit itself is OK -- it handles the bitmap properly.
> > The problem is the exceptional way to set up wValue for the mixer
> > unit, and I guess something like below could work.  It just stores the
> > part of wValue in an additional field, and use it for calculating the
> > correct wValue with MCN + UAC2_MU_MIXER in high byte.
> > 
> > Just compile tested, so not 100% sure whether it's correct.
> 
> ... and this version was obviously half-baked, forgotten the
> counterpart.  A revised patch is below.

... or maybe a less cryptic version like below.


Takashi

-- 8< --
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 33a6a1281410..c6639a45fb24 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -335,6 +335,16 @@ static int get_ctl_value_v1(struct usb_mixer_elem_info *cval, int request,
 	return -EINVAL;
 }
 
+/* convert the given UAC1 wValue (ICN+1|OCN+1) to UAC2 MCN */
+static unsigned int to_mcn(const struct usb_mixer_elem_info *cval,
+			   unsigned int validx)
+{
+	unsigned char m = (validx >> 8) & 0xff;
+	unsigned char v = validx & 0xff;
+
+	return (m - 1) * cval->num_outputs * (v - 1);
+}
+
 static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 			    int validx, int *value_ret)
 {
@@ -347,6 +357,10 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 
 	val_size = uac2_ctl_value_size(cval->val_type);
 
+	/* correct wValue for UAC2 mixer control with MCN */
+	if (cval->v2_mixer)
+		validx =(UAC2_MU_MIXER << 8) | to_mcn(cval, validx);
+
 	if (request == UAC_GET_CUR) {
 		bRequest = UAC2_CS_CUR;
 		size = val_size;
@@ -478,6 +492,10 @@ int snd_usb_mixer_set_ctl_value(struct usb_mixer_elem_info *cval,
 		}
 
 		request = UAC2_CS_CUR;
+
+		/* correct wValue for UAC2 mixer control with MCN */
+		if (cval->v2_mixer)
+			validx =(UAC2_MU_MIXER << 8) | to_mcn(cval, validx);
 	}
 
 	value_set = convert_bytes_value(cval, value_set);
@@ -2345,6 +2363,10 @@ static void build_mixer_unit_ctl(struct mixer_build *state,
 
 	snd_usb_mixer_elem_init_std(&cval->head, state->mixer, unitid);
 	cval->control = in_ch + 1; /* based on 1 */
+	if (state->mixer->protocol == UAC_VERSION_2 ||
+	    state->mixer->protocol == UAC_VERSION_3)
+		cval->v2_mixer = true;
+	cval->num_outputs = num_outs;
 	cval->val_type = USB_MIXER_S16;
 	for (i = 0; i < num_outs; i++) {
 		__u8 *c = uac_mixer_unit_bmControls(desc, state->mixer->protocol);
diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 037b446d8b6f..cf45c39cbccc 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -97,6 +97,8 @@ struct usb_mixer_elem_info {
 	u8 initialized;
 	u8 min_mute;
 	u8 get_cur_broken;
+	u8 num_outputs;
+	bool v2_mixer;
 	void *private_data;
 };