[RFC] ASoC: max98373: don't access volatile registers in bias level off

[Bard Liao]

We will set regcache_cache_only true in suspend. As a result, regmap_read
will return error when we try to read volatile registers in suspend.
Besides, it doesn't make sense to read feedback data when codec is not
active. To avoid the regmap_read error, this patch try to return a fake
value when kcontrol _get is called in suspend.
However, the question is what is the "correct" behavior when we try to
read a volatile register when cache only is set.
1. return an error code to signal codec is not available as what we have
now.
2. return a fake value like what this patch do.
3. wake-up the codec and always return a valid value.

Signed-off-by: Bard Liao <yung-chuan.liao at linux.intel.com>
---
 sound/soc/codecs/max98373.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/sound/soc/codecs/max98373.c b/sound/soc/codecs/max98373.c
index 929bb1798c43..07494e40c296 100644
--- a/sound/soc/codecs/max98373.c
+++ b/sound/soc/codecs/max98373.c
@@ -168,6 +168,23 @@ static SOC_ENUM_SINGLE_DECL(max98373_adc_samplerate_enum,
 			    MAX98373_R2051_MEAS_ADC_SAMPLING_RATE, 0,
 			    max98373_ADC_samplerate_text);
 
+static int max98373_feedback_get(struct snd_kcontrol *kcontrol,
+				 struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
+
+	if (snd_soc_component_get_bias_level(component) == SND_SOC_BIAS_OFF) {
+		/*
+		 * We can't get the feedback data when codec is off, set
+		 * value = 0 and return 0 to avoid error.
+		 */
+		ucontrol->value.integer.value[0] = 0;
+		return 0;
+	}
+
+	return snd_soc_put_volsw(kcontrol, ucontrol);
+}
+
 static const struct snd_kcontrol_new max98373_snd_controls[] = {
 SOC_SINGLE("Digital Vol Sel Switch", MAX98373_R203F_AMP_DSP_CFG,
 	MAX98373_AMP_VOL_SEL_SHIFT, 1, 0),
@@ -209,8 +226,10 @@ SOC_SINGLE("ADC PVDD FLT Switch", MAX98373_R2052_MEAS_ADC_PVDD_FLT_CFG,
 	MAX98373_FLT_EN_SHIFT, 1, 0),
 SOC_SINGLE("ADC TEMP FLT Switch", MAX98373_R2053_MEAS_ADC_THERM_FLT_CFG,
 	MAX98373_FLT_EN_SHIFT, 1, 0),
-SOC_SINGLE("ADC PVDD", MAX98373_R2054_MEAS_ADC_PVDD_CH_READBACK, 0, 0xFF, 0),
-SOC_SINGLE("ADC TEMP", MAX98373_R2055_MEAS_ADC_THERM_CH_READBACK, 0, 0xFF, 0),
+SOC_SINGLE_EXT("ADC PVDD", MAX98373_R2054_MEAS_ADC_PVDD_CH_READBACK, 0, 0xFF, 0,
+	max98373_feedback_get, NULL),
+SOC_SINGLE_EXT("ADC TEMP", MAX98373_R2055_MEAS_ADC_THERM_CH_READBACK, 0, 0xFF, 0,
+	max98373_feedback_get, NULL),
 SOC_SINGLE("ADC PVDD FLT Coeff", MAX98373_R2052_MEAS_ADC_PVDD_FLT_CFG,
 	0, 0x3, 0),
 SOC_SINGLE("ADC TEMP FLT Coeff", MAX98373_R2053_MEAS_ADC_THERM_FLT_CFG,
@@ -226,7 +245,8 @@ SOC_SINGLE("BDE LVL1 Thresh", MAX98373_R2097_BDE_L1_THRESH, 0, 0xFF, 0),
 SOC_SINGLE("BDE LVL2 Thresh", MAX98373_R2098_BDE_L2_THRESH, 0, 0xFF, 0),
 SOC_SINGLE("BDE LVL3 Thresh", MAX98373_R2099_BDE_L3_THRESH, 0, 0xFF, 0),
 SOC_SINGLE("BDE LVL4 Thresh", MAX98373_R209A_BDE_L4_THRESH, 0, 0xFF, 0),
-SOC_SINGLE("BDE Active Level", MAX98373_R20B6_BDE_CUR_STATE_READBACK, 0, 8, 0),
+SOC_SINGLE_EXT("BDE Active Level", MAX98373_R20B6_BDE_CUR_STATE_READBACK, 0, 8, 0,
+	max98373_feedback_get, NULL),
 SOC_SINGLE("BDE Clip Mode Switch", MAX98373_R2092_BDE_CLIPPER_MODE, 0, 1, 0),
 SOC_SINGLE("BDE Thresh Hysteresis", MAX98373_R209B_BDE_THRESH_HYST, 0, 0xFF, 0),
 SOC_SINGLE("BDE Hold Time", MAX98373_R2090_BDE_LVL_HOLD, 0, 0xFF, 0),
-- 
2.17.1