ASoC: twl6040: Add digital mute support

To reduce pop noise during playback stream start and stop the codec needs
to have the digital_mute callback implemented.
The codec need to be muted before the CPU dai has been stopped (McPDM).
Stopping the McPDM will generate a pop on the codec since no signal on the
PDM bus means full negative amplitude.
By managing the mute/unmute state of the outputs we can decrease the amount
of pop noise when playback starts or stops.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/codecs/twl6040.c

@@ -75,6 +75,8 @@ struct twl6040_data {
 	int pll_power_mode;
 	int hs_power_mode;
 	int hs_power_mode_locked;
+	bool dl1_unmuted;
+	bool dl2_unmuted;
 	unsigned int clk_in;
 	unsigned int sysclk;
 	struct twl6040_jack_data hs_jack;
@@ -228,6 +230,25 @@ static int twl6040_read_reg_volatile(struct snd_soc_codec *codec,
 	return value;
 }
 
+static bool twl6040_is_path_unmuted(struct snd_soc_codec *codec,
+				    unsigned int reg)
+{
+	struct twl6040_data *priv = snd_soc_codec_get_drvdata(codec);
+
+	switch (reg) {
+	case TWL6040_REG_HSLCTL:
+	case TWL6040_REG_HSRCTL:
+	case TWL6040_REG_EARCTL:
+		/* DL1 path */
+		return priv->dl1_unmuted;
+	case TWL6040_REG_HFLCTL:
+	case TWL6040_REG_HFRCTL:
+		return priv->dl2_unmuted;
+	default:
+		return 1;
+	};
+}
+
 /*
  * write to the twl6040 register space
  */
@@ -240,7 +261,8 @@ static int twl6040_write(struct snd_soc_codec *codec,
 		return -EIO;
 
 	twl6040_write_reg_cache(codec, reg, value);
-	if (likely(reg < TWL6040_REG_SW_SHADOW))
+	if (likely(reg < TWL6040_REG_SW_SHADOW) &&
+	    twl6040_is_path_unmuted(codec, reg))
 		return twl6040_reg_write(twl6040, reg, value);
 	else
 		return 0;
@@ -1034,11 +1056,78 @@ static int twl6040_set_dai_sysclk(struct snd_soc_dai *codec_dai,
 	return 0;
 }
 
+static void twl6040_mute_path(struct snd_soc_codec *codec, enum twl6040_dai_id id,
+			     int mute)
+{
+	struct twl6040 *twl6040 = codec->control_data;
+	struct twl6040_data *priv = snd_soc_codec_get_drvdata(codec);
+	int hslctl, hsrctl, earctl;
+	int hflctl, hfrctl;
+
+	switch (id) {
+	case TWL6040_DAI_DL1:
+		hslctl = twl6040_read_reg_cache(codec, TWL6040_REG_HSLCTL);
+		hsrctl = twl6040_read_reg_cache(codec, TWL6040_REG_HSRCTL);
+		earctl = twl6040_read_reg_cache(codec, TWL6040_REG_EARCTL);
+
+		if (mute) {
+			/* Power down drivers and DACs */
+			earctl &= ~0x01;
+			hslctl &= ~(TWL6040_HSDRVENA | TWL6040_HSDACENA);
+			hsrctl &= ~(TWL6040_HSDRVENA | TWL6040_HSDACENA);
+
+		}
+
+		twl6040_reg_write(twl6040, TWL6040_REG_EARCTL, earctl);
+		twl6040_reg_write(twl6040, TWL6040_REG_HSLCTL, hslctl);
+		twl6040_reg_write(twl6040, TWL6040_REG_HSRCTL, hsrctl);
+		priv->dl1_unmuted = !mute;
+		break;
+	case TWL6040_DAI_DL2:
+		hflctl = twl6040_read_reg_cache(codec, TWL6040_REG_HFLCTL);
+		hfrctl = twl6040_read_reg_cache(codec, TWL6040_REG_HFRCTL);
+
+		if (mute) {
+			/* Power down drivers and DACs */
+			hflctl &= ~(TWL6040_HFDACENA | TWL6040_HFPGAENA |
+				    TWL6040_HFDRVENA);
+			hfrctl &= ~(TWL6040_HFDACENA | TWL6040_HFPGAENA |
+				    TWL6040_HFDRVENA);
+		}
+
+		twl6040_reg_write(twl6040, TWL6040_REG_HFLCTL, hflctl);
+		twl6040_reg_write(twl6040, TWL6040_REG_HFRCTL, hfrctl);
+		priv->dl2_unmuted = !mute;
+		break;
+	default:
+		break;
+	};
+}
+
+static int twl6040_digital_mute(struct snd_soc_dai *dai, int mute)
+{
+	switch (dai->id) {
+	case TWL6040_DAI_LEGACY:
+		twl6040_mute_path(dai->codec, TWL6040_DAI_DL1, mute);
+		twl6040_mute_path(dai->codec, TWL6040_DAI_DL2, mute);
+		break;
+	case TWL6040_DAI_DL1:
+	case TWL6040_DAI_DL2:
+		twl6040_mute_path(dai->codec, dai->id, mute);
+		break;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
 static const struct snd_soc_dai_ops twl6040_dai_ops = {
 	.startup	= twl6040_startup,
 	.hw_params	= twl6040_hw_params,
 	.prepare	= twl6040_prepare,
 	.set_sysclk	= twl6040_set_dai_sysclk,
+	.digital_mute	= twl6040_digital_mute,
 };
 
 static struct snd_soc_dai_driver twl6040_dai[] = {