ASoC: tas6424: Add support for the mute pin

mute can be connected to GPIO. In that case we have to drive it to the
correct value
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/ti,tas6424.txt

@@ -7,6 +7,7 @@ Required properties:
 	- reg: I2C slave address
 	- sound-dai-cells: must be equal to 0
 	- standby-gpios: GPIO used to shut the TAS6424 down.
+	- mute-gpios: GPIO used to mute all the outputs
 
 Example:
 

sound/soc/codecs/tas6424.c

@@ -45,6 +45,7 @@ struct tas6424_data {
 	unsigned int last_fault2;
 	unsigned int last_warn;
 	struct gpio_desc *standby_gpio;
+	struct gpio_desc *mute_gpio;
 };
 
 /*
@@ -251,10 +252,16 @@ static int tas6424_set_dai_tdm_slot(struct snd_soc_dai *dai,
 static int tas6424_mute(struct snd_soc_dai *dai, int mute)
 {
 	struct snd_soc_component *component = dai->component;
+	struct tas6424_data *tas6424 = snd_soc_component_get_drvdata(component);
 	unsigned int val;
 
 	dev_dbg(component->dev, "%s() mute=%d\n", __func__, mute);
 
+	if (tas6424->mute_gpio) {
+		gpiod_set_value_cansleep(tas6424->mute_gpio, mute);
+		return 0;
+	}
+
 	if (mute)
 		val = TAS6424_ALL_STATE_MUTE;
 	else
@@ -289,6 +296,7 @@ static int tas6424_power_on(struct snd_soc_component *component)
 {
 	struct tas6424_data *tas6424 = snd_soc_component_get_drvdata(component);
 	int ret;
+	u8 chan_states;
 
 	ret = regulator_bulk_enable(ARRAY_SIZE(tas6424->supplies),
 				    tas6424->supplies);
@@ -305,7 +313,18 @@ static int tas6424_power_on(struct snd_soc_component *component)
 		return ret;
 	}
 
-	snd_soc_component_write(component, TAS6424_CH_STATE_CTRL, TAS6424_ALL_STATE_MUTE);
+	if (tas6424->mute_gpio) {
+		gpiod_set_value_cansleep(tas6424->mute_gpio, 0);
+		/*
+		 * channels are muted via the mute pin.  Don't also mute
+		 * them via the registers so that subsequent register
+		 * access is not necessary to un-mute the channels
+		 */
+		chan_states = TAS6424_ALL_STATE_PLAY;
+	} else {
+		chan_states = TAS6424_ALL_STATE_MUTE;
+	}
+	snd_soc_component_write(component, TAS6424_CH_STATE_CTRL, chan_states);
 
 	/* any time we come out of HIZ, the output channels automatically run DC
 	 * load diagnostics, wait here until this completes
@@ -645,6 +664,22 @@ static int tas6424_i2c_probe(struct i2c_client *client,
 		tas6424->standby_gpio = NULL;
 	}
 
+	/*
+	 * Get control of the mute pin and set it HIGH in order to start with
+	 * all the output muted.
+	 * Note: The actual pin polarity is taken care of in the GPIO lib
+	 * according the polarity specified in the DTS.
+	 */
+	tas6424->mute_gpio = devm_gpiod_get_optional(dev, "mute",
+						      GPIOD_OUT_HIGH);
+	if (IS_ERR(tas6424->mute_gpio)) {
+		if (PTR_ERR(tas6424->mute_gpio) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
+		dev_info(dev, "failed to get nmute GPIO: %ld\n",
+			PTR_ERR(tas6424->mute_gpio));
+		tas6424->mute_gpio = NULL;
+	}
+
 	for (i = 0; i < ARRAY_SIZE(tas6424->supplies); i++)
 		tas6424->supplies[i].supply = tas6424_supply_names[i];
 	ret = devm_regulator_bulk_get(dev, ARRAY_SIZE(tas6424->supplies),