[PATCH v3 2/3] ALSA: usb-audio: Fix UAC2 mixer unit request handling

[Takashi Iwai <tiwai@suse.de>]

For a request for a Mixer Unit on UAC2 (also UAC3), the wValue is
different from UAC1 and an incompatible value must be passed.
Namely, UAC1 takes a word consisting of 1-based input channel in the
high byte and 1-based output channel in the low byte.
Meanwhile, UAC2/3 takes UAC2_MU_MIXER in the high byte and a MCN
(0-based bit position of input/output channels) in the low byte.
The current driver implementation blindly assumes the UAC1 way, hence
it would cause a firmware error.

This patch attempts to implement the conversion to UAC2 MCN at
get_ctl_value_v2() and snd_usb_mixer_set_ctl_value() for mixer units.
At the points above, the old wValue containing ICN and OCN is
converted to the corresponding MCN, and it's used as the proper
wValue.

Reported-by: Zipdox <zipdox@zipdox.net>
Closes: https://lore.kernel.org/d46fcac6-bd7e-4fc4-95e1-4e8d39f92ad3@zipdox.net
Fixes: 23caaf19b11e ("ALSA: usb-mixer: Add support for Audio Class v2.0")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
v2->v3: no change

 sound/usb/mixer.c | 23 +++++++++++++++++++++++
 sound/usb/mixer.h |  2 ++
 2 files changed, 25 insertions(+)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ddfd7e01a3ef..a8bdd1696a20 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -335,6 +335,17 @@ static int get_ctl_value_v1(struct usb_mixer_elem_info *cval, int request,
 	return -EINVAL;
 }
 
+/* convert the given UAC1 wValue (ICN|OCN) to UAC2 MCN */
+static unsigned char to_mcn(const struct usb_mixer_elem_info *cval,
+			    unsigned int validx)
+{
+	unsigned char m = (validx >> 8) & 0xff; /* 1-based input channel */
+	unsigned char v = validx & 0xff; /* 1-based output channel */
+
+	/* num_inputs * num_outputs is guaranteed to be < 256 */
+	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 +358,10 @@ 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 +493,10 @@ 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 +2364,10 @@ 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;
 };
 
-- 
2.55.0