ASoC: cs42l42: Add control for audio slow-start switch

This adds an ALSA control so that the slow-start audio ramp feature
can be disabled. This is useful for high-definition audio applications.

The register field is unusual in that it is a 3-bit field with only
two valid values, 000=off and 111=on.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20211101101006.13092-1-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/cs42l42.c

@@ -42,6 +42,7 @@ static const struct reg_default cs42l42_reg_defaults[] = {
 	{ CS42L42_SRC_CTL,			0x10 },
 	{ CS42L42_MCLK_CTL,			0x02 },
 	{ CS42L42_SFTRAMP_RATE,			0xA4 },
+	{ CS42L42_SLOW_START_ENABLE,		0x70 },
 	{ CS42L42_I2C_DEBOUNCE,			0x88 },
 	{ CS42L42_I2C_STRETCH,			0x03 },
 	{ CS42L42_I2C_TIMEOUT,			0xB7 },
@@ -177,6 +178,7 @@ static bool cs42l42_readable_register(struct device *dev, unsigned int reg)
 	case CS42L42_MCLK_STATUS:
 	case CS42L42_MCLK_CTL:
 	case CS42L42_SFTRAMP_RATE:
+	case CS42L42_SLOW_START_ENABLE:
 	case CS42L42_I2C_DEBOUNCE:
 	case CS42L42_I2C_STRETCH:
 	case CS42L42_I2C_TIMEOUT:
@@ -387,6 +389,28 @@ static const struct regmap_config cs42l42_regmap = {
 static DECLARE_TLV_DB_SCALE(adc_tlv, -9700, 100, true);
 static DECLARE_TLV_DB_SCALE(mixer_tlv, -6300, 100, true);
 
+static int cs42l42_slow_start_put(struct snd_kcontrol *kcontrol,
+				  struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_soc_component *component = snd_soc_kcontrol_component(kcontrol);
+	u8 val;
+
+	/* all bits of SLOW_START_EN much change together */
+	switch (ucontrol->value.integer.value[0]) {
+	case 0:
+		val = 0;
+		break;
+	case 1:
+		val = CS42L42_SLOW_START_EN_MASK;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return snd_soc_component_update_bits(component, CS42L42_SLOW_START_ENABLE,
+					     CS42L42_SLOW_START_EN_MASK, val);
+}
+
 static const char * const cs42l42_hpf_freq_text[] = {
 	"1.86Hz", "120Hz", "235Hz", "466Hz"
 };
@@ -431,7 +455,11 @@ static const struct snd_kcontrol_new cs42l42_snd_controls[] = {
 				CS42L42_DAC_HPF_EN_SHIFT, true, false),
 	SOC_DOUBLE_R_TLV("Mixer Volume", CS42L42_MIXER_CHA_VOL,
 			 CS42L42_MIXER_CHB_VOL, CS42L42_MIXER_CH_VOL_SHIFT,
-				0x3f, 1, mixer_tlv)
+				0x3f, 1, mixer_tlv),
+
+	SOC_SINGLE_EXT("Slow Start Switch", CS42L42_SLOW_START_ENABLE,
+			CS42L42_SLOW_START_EN_SHIFT, true, false,
+			snd_soc_get_volsw, cs42l42_slow_start_put),
 };
 
 static int cs42l42_hp_adc_ev(struct snd_soc_dapm_widget *w,

sound/soc/codecs/cs42l42.h

@@ -62,6 +62,9 @@
 #define CS42L42_INTERNAL_FS_MASK	(1 << CS42L42_INTERNAL_FS_SHIFT)
 
 #define CS42L42_SFTRAMP_RATE		(CS42L42_PAGE_10 + 0x0A)
+#define CS42L42_SLOW_START_ENABLE	(CS42L42_PAGE_10 + 0x0B)
+#define CS42L42_SLOW_START_EN_MASK	GENMASK(6, 4)
+#define CS42L42_SLOW_START_EN_SHIFT	4
 #define CS42L42_I2C_DEBOUNCE		(CS42L42_PAGE_10 + 0x0E)
 #define CS42L42_I2C_STRETCH		(CS42L42_PAGE_10 + 0x0F)
 #define CS42L42_I2C_TIMEOUT		(CS42L42_PAGE_10 + 0x10)