ALSA: scarlett2: Add support for custom Gen 4 Direct Monitor mixes

The mixes used by Direct Monitor feature on the Scarlett 4th Gen Solo
and 2i2 interfaces are configurable. This patch adds ALSA controls for
the gains which are copied to the mixer when Direct Monitor is
enabled.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/96282a805b45f04560e5923d170745363906b7f3.1703612638.git.g@b4.vu

sound/usb/mixer_scarlett2.c

@@ -213,6 +213,13 @@ static const u16 scarlett2_mixer_values[SCARLETT2_MIXER_VALUE_COUNT] = {
 /* Maximum number of mixer gain controls */
 #define SCARLETT2_MIX_MAX (SCARLETT2_INPUT_MIX_MAX * SCARLETT2_OUTPUT_MIX_MAX)
 
+/* Maximum number of direct monitor mixer gain controls
+ * 1 (Solo) or 2 (2i2) direct monitor selections (Mono & Stereo)
+ * 2 Mix outputs (A/Left & B/Right)
+ * 4 Mix inputs
+ */
+#define SCARLETT2_MONITOR_MIX_MAX (2 * 2 * 4)
+
 /* Maximum size of the data in the USB mux assignment message:
  * 20 inputs, 20 outputs, 25 matrix inputs, 12 spare
  */
@@ -344,6 +351,7 @@ enum {
 	SCARLETT2_CONFIG_INPUT_LINK_SWITCH,
 	SCARLETT2_CONFIG_POWER_EXT,
 	SCARLETT2_CONFIG_POWER_STATUS,
+	SCARLETT2_CONFIG_DIRECT_MONITOR_GAIN,
 	SCARLETT2_CONFIG_COUNT
 };
 
@@ -742,6 +750,7 @@ struct scarlett2_data {
 	u8 num_mix_in;
 	u8 num_mix_out;
 	u8 num_line_out;
+	u8 num_monitor_mix_ctls;
 	u32 firmware_version;
 	u8 flash_segment_nums[SCARLETT2_SEGMENT_ID_COUNT];
 	u8 flash_segment_blocks[SCARLETT2_SEGMENT_ID_COUNT];
@@ -812,6 +821,7 @@ struct scarlett2_data {
 	struct snd_kcontrol *power_status_ctl;
 	u8 mux[SCARLETT2_MUX_MAX];
 	u8 mix[SCARLETT2_MIX_MAX];
+	u8 monitor_mix[SCARLETT2_MONITOR_MIX_MAX];
 };
 
 /*** Model-specific data ***/
@@ -5108,6 +5118,28 @@ static int scarlett2_update_direct_monitor(struct usb_mixer_interface *mixer)
 		1, &private->direct_monitor_switch);
 }
 
+static int scarlett2_update_monitor_mix(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_data *private = mixer->private_data;
+	int err, i;
+	u16 mix_values[SCARLETT2_MONITOR_MIX_MAX];
+
+	if (!private->num_monitor_mix_ctls)
+		return 0;
+
+	err = scarlett2_usb_get_config(
+		mixer, SCARLETT2_CONFIG_DIRECT_MONITOR_GAIN,
+		private->num_monitor_mix_ctls, mix_values);
+	if (err < 0)
+		return err;
+
+	for (i = 0; i < private->num_monitor_mix_ctls; i++)
+		private->monitor_mix[i] = scarlett2_mixer_value_to_db(
+			mix_values[i]);
+
+	return 0;
+}
+
 static int scarlett2_direct_monitor_ctl_get(
 	struct snd_kcontrol *kctl, struct snd_ctl_elem_value *ucontrol)
 {
@@ -5201,11 +5233,70 @@ static const struct snd_kcontrol_new scarlett2_direct_monitor_ctl[2] = {
 	}
 };
 
-static int scarlett2_add_direct_monitor_ctl(struct usb_mixer_interface *mixer)
+static int scarlett2_monitor_mix_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;
+
+	ucontrol->value.integer.value[0] = private->monitor_mix[elem->control];
+
+	return 0;
+}
+
+static int scarlett2_monitor_mix_ctl_put(struct snd_kcontrol *kctl,
+					 struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_data *private = mixer->private_data;
+	int oval, val, err = 0;
+	int index = elem->control;
+
+	mutex_lock(&private->data_mutex);
+
+	if (private->hwdep_in_use) {
+		err = -EBUSY;
+		goto unlock;
+	}
+
+	oval = private->monitor_mix[index];
+	val = clamp(ucontrol->value.integer.value[0],
+		    0L, (long)SCARLETT2_MIXER_MAX_VALUE);
+
+	if (oval == val)
+		goto unlock;
+
+	private->monitor_mix[index] = val;
+	err = scarlett2_usb_set_config(
+		mixer, SCARLETT2_CONFIG_DIRECT_MONITOR_GAIN,
+		index, scarlett2_mixer_values[val]);
+	if (err == 0)
+		err = 1;
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const struct snd_kcontrol_new scarlett2_monitor_mix_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+		  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+	.name = "",
+	.info = scarlett2_mixer_ctl_info,
+	.get  = scarlett2_monitor_mix_ctl_get,
+	.put  = scarlett2_monitor_mix_ctl_put,
+	.private_value = SCARLETT2_MIXER_MAX_DB, /* max value */
+	.tlv = { .p = db_scale_scarlett2_mixer }
+};
+
+static int scarlett2_add_direct_monitor_ctls(struct usb_mixer_interface *mixer)
 {
 	struct scarlett2_data *private = mixer->private_data;
 	const struct scarlett2_device_info *info = private->info;
 	const char *s;
+	int err, i, j, k, index;
 
 	if (!info->direct_monitor)
 		return 0;
@@ -5214,9 +5305,47 @@ static int scarlett2_add_direct_monitor_ctl(struct usb_mixer_interface *mixer)
 	      ? "Direct Monitor Playback Switch"
 	      : "Direct Monitor Playback Enum";
 
-	return scarlett2_add_new_ctl(
+	err = scarlett2_add_new_ctl(
 		mixer, &scarlett2_direct_monitor_ctl[info->direct_monitor - 1],
 		0, 1, s, &private->direct_monitor_ctl);
+	if (err < 0)
+		return err;
+
+	if (!private->num_monitor_mix_ctls)
+		return 0;
+
+	/* 1 or 2 direct monitor selections (Mono & Stereo) */
+	for (i = 0, index = 0; i < info->direct_monitor; i++) {
+		const char * const format =
+			"Monitor %sMix %c Input %02d Playback Volume";
+		const char *mix_type;
+
+		if (info->direct_monitor == 1)
+			mix_type = "";
+		else if (i == 0)
+			mix_type = "1 ";
+		else
+			mix_type = "2 ";
+
+		/* 2 Mix outputs, A/Left & B/Right */
+		for (j = 0; j < 2; j++)
+
+			/* Mix inputs */
+			for (k = 0; k < private->num_mix_in; k++, index++) {
+				char name[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+
+				snprintf(name, sizeof(name), format,
+					 mix_type, 'A' + j, k + 1);
+
+				err = scarlett2_add_new_ctl(
+					mixer, &scarlett2_monitor_mix_ctl,
+					index, 1, name, NULL);
+				if (err < 0)
+					return err;
+			}
+	}
+
+	return 0;
 }
 
 /*** Mux Source Selection Controls ***/
@@ -5708,6 +5837,10 @@ static void scarlett2_count_io(struct scarlett2_data *private)
 	/* Number of analogue line outputs */
 	private->num_line_out =
 		port_count[SCARLETT2_PORT_TYPE_ANALOGUE][SCARLETT2_PORT_OUT];
+
+	/* Number of monitor mix controls */
+	private->num_monitor_mix_ctls =
+		info->direct_monitor * 2 * private->num_mix_in;
 }
 
 /* Look through the interface descriptors for the Focusrite Control
@@ -5938,6 +6071,10 @@ static int scarlett2_read_configs(struct usb_mixer_interface *mixer)
 	if (!scarlett2_has_mixer(private))
 		return 0;
 
+	err = scarlett2_update_monitor_mix(mixer);
+	if (err < 0)
+		return err;
+
 	err = scarlett2_update_monitor_other(mixer);
 	if (err < 0)
 		return err;
@@ -6474,8 +6611,8 @@ static int snd_scarlett2_controls_create(
 	if (err < 0)
 		return err;
 
-	/* Create the direct monitor control */
-	err = scarlett2_add_direct_monitor_ctl(mixer);
+	/* Create the direct monitor control(s) */
+	err = scarlett2_add_direct_monitor_ctls(mixer);
 	if (err < 0)
 		return err;