ASoC: Add CODEC volatile register operation

Add a volatile_register() operation to the CODEC structure providing a
standard operation to query if a register is volatile. This will be used
to factor out the register cache I/O operations for the CODECs.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

include/sound/soc.h

@@ -191,6 +191,7 @@ int snd_soc_register_platform(struct snd_soc_platform *platform);
 void snd_soc_unregister_platform(struct snd_soc_platform *platform);
 int snd_soc_register_codec(struct snd_soc_codec *codec);
 void snd_soc_unregister_codec(struct snd_soc_codec *codec);
+int snd_soc_codec_volatile_register(struct snd_soc_codec *codec, int reg);
 
 #ifdef CONFIG_PM
 int snd_soc_suspend_device(struct device *dev);
@@ -361,6 +362,7 @@ struct snd_soc_codec {
 	int (*write)(struct snd_soc_codec *, unsigned int, unsigned int);
 	int (*display_register)(struct snd_soc_codec *, char *,
 				size_t, unsigned int);
+	int (*volatile_register)(unsigned int);
 	hw_write_t hw_write;
 	hw_read_t hw_read;
 	void *reg_cache;

sound/soc/soc-core.c

@@ -1125,6 +1125,23 @@ static int soc_new_pcm(struct snd_soc_device *socdev,
 	return ret;
 }
 
+/**
+ * snd_soc_codec_volatile_register: Report if a register is volatile.
+ *
+ * @codec: CODEC to query.
+ * @reg: Register to query.
+ *
+ * Boolean function indiciating if a CODEC register is volatile.
+ */
+int snd_soc_codec_volatile_register(struct snd_soc_codec *codec, int reg)
+{
+	if (codec->volatile_register)
+		return codec->volatile_register(reg);
+	else
+		return 0;
+}
+EXPORT_SYMBOL_GPL(snd_soc_codec_volatile_register);
+
 /* codec register dump */
 static ssize_t soc_codec_reg_show(struct snd_soc_codec *codec, char *buf)
 {