ASoC: intel/sdw_utils: Add volume limit to cs35l56 speakers

The volume control for cs35l56 speakers has a maximum gain of +12 dB.
However, for many use cases, this can cause distorted audio, depending
various factors, such as other signal-processing elements in the chain,
for example if the audio passes through a gain control before reaching
the amp or the signal path has been tuned for a particular maximum
gain in the amp.

In the case of systems which use the soc_sdw_* driver, audio will
likely be distorted in all cases above 0 dB, therefore add a volume
limit of 400, which is 0 dB maximum volume inside this driver.

The volume limit should be applied to both soundwire and soundwire
bridge configurations.

Signed-off-by: Stefan Binding <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Mark Brown <[email protected]>

Author: Stefan Binding

include/sound/soc_sdw_utils.h

@@ -226,6 +226,7 @@ int asoc_sdw_cs_amp_init(struct snd_soc_card *card,
 			 bool playback);
 int asoc_sdw_cs_spk_feedback_rtd_init(struct snd_soc_pcm_runtime *rtd,
 				      struct snd_soc_dai *dai);
+int asoc_sdw_cs35l56_volume_limit(struct snd_soc_card *card, const char *name_prefix);
 
 /* MAXIM codec support */
 int asoc_sdw_maxim_init(struct snd_soc_card *card,

sound/soc/sdw_utils/soc_sdw_bridge_cs35l56.c

@@ -60,6 +60,10 @@ static int asoc_sdw_bridge_cs35l56_asp_init(struct snd_soc_pcm_runtime *rtd)
 
 	/* 4 x 16-bit sample slots and FSYNC=48000, BCLK=3.072 MHz */
 	for_each_rtd_codec_dais(rtd, i, codec_dai) {
+		ret = asoc_sdw_cs35l56_volume_limit(card, codec_dai->component->name_prefix);
+		if (ret)
+			return ret;
+
 		ret = snd_soc_dai_set_tdm_slot(codec_dai, tx_mask, rx_mask, 4, 16);
 		if (ret < 0)
 			return ret;

sound/soc/sdw_utils/soc_sdw_cs_amp.c

@@ -16,6 +16,25 @@
 
 #define CODEC_NAME_SIZE	8
 #define CS_AMP_CHANNELS_PER_AMP	4
+#define CS35L56_SPK_VOLUME_0DB 400 /* 0dB Max */
+
+int asoc_sdw_cs35l56_volume_limit(struct snd_soc_card *card, const char *name_prefix)
+{
+	char *volume_ctl_name;
+	int ret;
+
+	volume_ctl_name = kasprintf(GFP_KERNEL, "%s Speaker Volume", name_prefix);
+	if (!volume_ctl_name)
+		return -ENOMEM;
+
+	ret = snd_soc_limit_volume(card, volume_ctl_name, CS35L56_SPK_VOLUME_0DB);
+	if (ret)
+		dev_err(card->dev, "%s limit set failed: %d\n", volume_ctl_name, ret);
+
+	kfree(volume_ctl_name);
+	return ret;
+}
+EXPORT_SYMBOL_NS(asoc_sdw_cs35l56_volume_limit, "SND_SOC_SDW_UTILS");
 
 int asoc_sdw_cs_spk_rtd_init(struct snd_soc_pcm_runtime *rtd, struct snd_soc_dai *dai)
 {
@@ -40,6 +59,11 @@ int asoc_sdw_cs_spk_rtd_init(struct snd_soc_pcm_runtime *rtd, struct snd_soc_dai
 
 		snprintf(widget_name, sizeof(widget_name), "%s SPK",
 			 codec_dai->component->name_prefix);
+
+		ret = asoc_sdw_cs35l56_volume_limit(card, codec_dai->component->name_prefix);
+		if (ret)
+			return ret;
+
 		ret = snd_soc_dapm_add_routes(&card->dapm, &route, 1);
 		if (ret)
 			return ret;