ALSA: hda: Use regcache_reg_cached() rather than open coding

The HDA driver intentionally drops repeated writes to registers in some
circumstances, beyond the suppression of noop writes that regmap does in
regmap_update_bits(). It does this by checking if the register is cached
before doing a regmap_update_bits(), now we have an API for querying this
directly use it directly rather than trying a read in cache only mode
making the code a little clearer.

Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230717-regmap-cache-check-v1-3-73ef688afae3@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: broonie

sound/hda/hdac_regmap.c

@@ -556,17 +556,14 @@ EXPORT_SYMBOL_GPL(snd_hdac_regmap_update_raw);
 static int reg_raw_update_once(struct hdac_device *codec, unsigned int reg,
 			       unsigned int mask, unsigned int val)
 {
-	unsigned int orig;
-	int err;
+	int err = 0;
 
 	if (!codec->regmap)
 		return reg_raw_update(codec, reg, mask, val);
 
 	mutex_lock(&codec->regmap_lock);
-	regcache_cache_only(codec->regmap, true);
-	err = regmap_read(codec->regmap, reg, &orig);
-	regcache_cache_only(codec->regmap, false);
-	if (err < 0)
+	/* Discard any updates to already initialised registers. */
+	if (!regcache_reg_cached(codec->regmap, reg))
 		err = regmap_update_bits(codec->regmap, reg, mask, val);
 	mutex_unlock(&codec->regmap_lock);
 	return err;