ASoC: da7219: Fix change notifications for tone generator frequency

The tone generator frequency control just returns 0 on successful write,
not a boolean value indicating if there was a change or not.  Compare
what was written with the value that was there previously so that
notifications are generated appropriately when the value changes.
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220420133437.569229-1-broonie@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/da7219.c

@@ -446,7 +446,7 @@ static int da7219_tonegen_freq_put(struct snd_kcontrol *kcontrol,
 	struct soc_mixer_control *mixer_ctrl =
 		(struct soc_mixer_control *) kcontrol->private_value;
 	unsigned int reg = mixer_ctrl->reg;
-	__le16 val;
+	__le16 val_new, val_old;
 	int ret;
 
 	/*
@@ -454,13 +454,19 @@ static int da7219_tonegen_freq_put(struct snd_kcontrol *kcontrol,
 	 * Therefore we need to convert to little endian here to align with
 	 * HW registers.
 	 */
-	val = cpu_to_le16(ucontrol->value.integer.value[0]);
+	val_new = cpu_to_le16(ucontrol->value.integer.value[0]);
 
 	mutex_lock(&da7219->ctrl_lock);
-	ret = regmap_raw_write(da7219->regmap, reg, &val, sizeof(val));
+	ret = regmap_raw_read(da7219->regmap, reg, &val_old, sizeof(val_old));
+	if (ret == 0 && (val_old != val_new))
+		ret = regmap_raw_write(da7219->regmap, reg,
+				&val_new, sizeof(val_new));
 	mutex_unlock(&da7219->ctrl_lock);
 
-	return ret;
+	if (ret < 0)
+		return ret;
+
+	return val_old != val_new;
 }