ASoC: Add default snd_soc_default_writable_register() callback

By using struct snd_soc_reg_access for the read/write/vol attributes
of the registers, we provide callbacks that automatically determine whether
a given register is readable/writable or volatile.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/sound/soc/soc-cache.c b/sound/soc/soc-cache.c
index 258c3b2..1210a6f 100644
--- a/sound/soc/soc-cache.c
+++ b/sound/soc/soc-cache.c
@@ -1449,3 +1449,17 @@
 	return codec->driver->reg_access_default[index].read;
 }
 EXPORT_SYMBOL_GPL(snd_soc_default_readable_register);
+
+int snd_soc_default_writable_register(struct snd_soc_codec *codec,
+				      unsigned int reg)
+{
+	int index;
+
+	if (reg >= codec->driver->reg_cache_size)
+		return 1;
+	index = snd_soc_get_reg_access_index(codec, reg);
+	if (index < 0)
+		return 0;
+	return codec->driver->reg_access_default[index].write;
+}
+EXPORT_SYMBOL_GPL(snd_soc_default_writable_register);