ASoC: adau17x1: Cache writes when core clock is disabled

In some configurations, the dai registers get written before the bias
level is changed in the codec driver. This leads to a situation where
an initial write to the serial port register gets ignored, and future
writes may as well, since regmap thinks that the codec already holds the
value. More specifically, configuring the codec as i2s master would in
fact result in the codec running as slave, a situation where no i2s
clocks are generated and hence no data is transferred.

This change makes sure that regmap only caches writes when the core
clock is disabled, and syncs regmap whenever enabling the core clock
again.
Signed-off-by: Andreas Irestål <andire@axis.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/adau1761.c

@@ -456,13 +456,17 @@ static int adau1761_set_bias_level(struct snd_soc_codec *codec,
 	case SND_SOC_BIAS_PREPARE:
 		break;
 	case SND_SOC_BIAS_STANDBY:
+		regcache_cache_only(adau->regmap, false);
 		regmap_update_bits(adau->regmap, ADAU17X1_CLOCK_CONTROL,
 			ADAU17X1_CLOCK_CONTROL_SYSCLK_EN,
 			ADAU17X1_CLOCK_CONTROL_SYSCLK_EN);
+		if (snd_soc_codec_get_bias_level(codec) == SND_SOC_BIAS_OFF)
+			regcache_sync(adau->regmap);
 		break;
 	case SND_SOC_BIAS_OFF:
 		regmap_update_bits(adau->regmap, ADAU17X1_CLOCK_CONTROL,
 			ADAU17X1_CLOCK_CONTROL_SYSCLK_EN, 0);
+		regcache_cache_only(adau->regmap, true);
 		break;
 
 	}
@@ -783,6 +787,10 @@ int adau1761_probe(struct device *dev, struct regmap *regmap,
 	if (ret)
 		return ret;
 
+	/* Enable cache only mode as we could miss writes before bias level
+	 * reaches standby and the core clock is enabled */
+	regcache_cache_only(regmap, true);
+
 	return snd_soc_register_codec(dev, &adau1761_codec_driver, dai_drv, 1);
 }
 EXPORT_SYMBOL_GPL(adau1761_probe);