ALSA: usb-audio: scarlett2: Update mux controls to allow updates

Enabling/disabling speaker switching will update the mux
configuration. To prepare for this, add a private->mux_updated flag
and update the scarlett2_mux_src_enum_ctl_get() callback to check it.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/5ce3bb9fe4006b550d18c783c5ff640fe0bfbfcb.1624379707.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -378,6 +378,7 @@ struct scarlett2_data {
 	u8 vol_updated;
 	u8 input_other_updated;
 	u8 monitor_other_updated;
+	u8 mux_updated;
 	u8 sync;
 	u8 master_vol;
 	u8 vol[SCARLETT2_ANALOGUE_MAX];
@@ -1446,6 +1447,8 @@ static int scarlett2_usb_get_mux(struct usb_mixer_interface *mixer)
 
 	__le32 data[SCARLETT2_MUX_MAX];
 
+	private->mux_updated = 0;
+
 	req.num = 0;
 	req.count = cpu_to_le16(count);
 
@@ -2799,7 +2802,8 @@ static int scarlett2_mux_src_enum_ctl_get(struct snd_kcontrol *kctl,
 					  struct snd_ctl_elem_value *ucontrol)
 {
 	struct usb_mixer_elem_info *elem = kctl->private_data;
-	struct scarlett2_data *private = elem->head.mixer->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_data *private = mixer->private_data;
 	const struct scarlett2_device_info *info = private->info;
 	const int (*port_count)[SCARLETT2_PORT_DIRNS] = info->port_count;
 	int line_out_count =
@@ -2809,7 +2813,12 @@ static int scarlett2_mux_src_enum_ctl_get(struct snd_kcontrol *kctl,
 	if (index < line_out_count)
 		index = line_out_remap(private, index);
 
+	mutex_lock(&private->data_mutex);
+	if (private->mux_updated)
+		scarlett2_usb_get_mux(mixer);
 	ucontrol->value.enumerated.item[0] = private->mux[index];
+	mutex_unlock(&private->data_mutex);
+
 	return 0;
 }