ASoC: hdmi-codec: re-introduce mutex locking

Replace the bit atomic operations by a mutex to ensure only one dai
at a time is active on the hdmi codec.

This is a follow up on change:
3fcf94ef ("ASoC: hdmi-codec: remove reference to the current substream")
Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/hdmi-codec.c

@@ -281,7 +281,7 @@ struct hdmi_codec_priv {
 	uint8_t eld[MAX_ELD_BYTES];
 	struct snd_pcm_chmap *chmap_info;
 	unsigned int chmap_idx;
-	unsigned long busy;
+	struct mutex lock;
 };
 
 static const struct snd_soc_dapm_widget hdmi_widgets[] = {
@@ -395,8 +395,8 @@ static int hdmi_codec_startup(struct snd_pcm_substream *substream,
 	struct hdmi_codec_priv *hcp = snd_soc_dai_get_drvdata(dai);
 	int ret = 0;
 
-	ret = test_and_set_bit(0, &hcp->busy);
-	if (ret) {
+	ret = mutex_trylock(&hcp->lock);
+	if (!ret) {
 		dev_err(dai->dev, "Only one simultaneous stream supported!\n");
 		return -EINVAL;
 	}
@@ -424,7 +424,7 @@ static int hdmi_codec_startup(struct snd_pcm_substream *substream,
 
 err:
 	/* Release the exclusive lock on error */
-	clear_bit(0, &hcp->busy);
+	mutex_unlock(&hcp->lock);
 	return ret;
 }
 
@@ -436,7 +436,7 @@ static void hdmi_codec_shutdown(struct snd_pcm_substream *substream,
 	hcp->chmap_idx = HDMI_CODEC_CHMAP_IDX_UNKNOWN;
 	hcp->hcd.ops->audio_shutdown(dai->dev->parent, hcp->hcd.data);
 
-	clear_bit(0, &hcp->busy);
+	mutex_unlock(&hcp->lock);
 }
 
 static int hdmi_codec_hw_params(struct snd_pcm_substream *substream,
@@ -773,6 +773,8 @@ static int hdmi_codec_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	hcp->hcd = *hcd;
+	mutex_init(&hcp->lock);
+
 	daidrv = devm_kcalloc(dev, dai_count, sizeof(*daidrv), GFP_KERNEL);
 	if (!daidrv)
 		return -ENOMEM;