ASoC: hdmi-codec: re-introduce mutex locking again

The dai codec needs to ensure that on one dai is used at any time.
This is currently protected by bit atomic operation. With this change,
it done with a mutex instead.

This change is not about functionality or efficiency. It is done with
the hope that it help maintainability in the future.

Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20191206103542.485224-1-jbrunet@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/hdmi-codec.c

@@ -274,7 +274,8 @@ 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;
+	bool busy;
 	struct snd_soc_jack *jack;
 	unsigned int jack_status;
 };
@@ -390,9 +391,10 @@ 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) {
+	mutex_lock(&hcp->lock);
+	if (hcp->busy) {
 		dev_err(dai->dev, "Only one simultaneous stream supported!\n");
+		mutex_unlock(&hcp->lock);
 		return -EINVAL;
 	}
 
@@ -405,21 +407,21 @@ static int hdmi_codec_startup(struct snd_pcm_substream *substream,
 	if (hcp->hcd.ops->get_eld) {
 		ret = hcp->hcd.ops->get_eld(dai->dev->parent, hcp->hcd.data,
 					    hcp->eld, sizeof(hcp->eld));
+		if (ret)
+			goto err;
+
+		ret = snd_pcm_hw_constraint_eld(substream->runtime, hcp->eld);
+		if (ret)
+			goto err;
 
-		if (!ret) {
-			ret = snd_pcm_hw_constraint_eld(substream->runtime,
-							hcp->eld);
-			if (ret)
-				goto err;
-		}
 		/* Select chmap supported */
 		hdmi_codec_eld_chmap(hcp);
 	}
-	return 0;
+
+	hcp->busy = true;
 
 err:
-	/* Release the exclusive lock on error */
-	clear_bit(0, &hcp->busy);
+	mutex_unlock(&hcp->lock);
 	return ret;
 }
 
@@ -431,7 +433,9 @@ 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_lock(&hcp->lock);
+	hcp->busy = false;
+	mutex_unlock(&hcp->lock);
 }
 
 static int hdmi_codec_hw_params(struct snd_pcm_substream *substream,
@@ -811,6 +815,8 @@ 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;