ASoC: apple: mca: Add locking

In DAI ops, accesses to the native cluster (of the DAI), and to data of
clusters related to it by a DPCM frontend-backend link, should have
been synchronized by the 'pcm_mutex' lock at ASoC level.

What is not covered are the 'port_driver' accesses on foreign clusters
to which the current cluster has no a priori relation, so fill in
locking for that. (This should only matter in bizarre configurations of
sharing one MCA peripheral between ASoC cards.)

Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20220824160715.95779-5-povik+lin@cutebit.org
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/apple/mca.c

@@ -158,6 +158,9 @@ struct mca_data {
 	struct reset_control *rstc;
 	struct device_link *pd_link;
 
+	/* Mutex for accessing port_driver of foreign clusters */
+	struct mutex port_mutex;
+
 	int nclusters;
 	struct mca_cluster clusters[];
 };
@@ -296,16 +299,21 @@ static bool mca_fe_clocks_in_use(struct mca_cluster *cl)
 	struct mca_cluster *be_cl;
 	int stream, i;
 
+	mutex_lock(&mca->port_mutex);
 	for (i = 0; i < mca->nclusters; i++) {
 		be_cl = &mca->clusters[i];
 
 		if (be_cl->port_driver != cl->no)
 			continue;
 
-		for_each_pcm_streams(stream)
-			if (be_cl->clocks_in_use[stream])
+		for_each_pcm_streams(stream) {
+			if (be_cl->clocks_in_use[stream]) {
+				mutex_unlock(&mca->port_mutex);
 				return true;
+			}
+		}
 	}
+	mutex_unlock(&mca->port_mutex);
 	return false;
 }
 
@@ -349,6 +357,11 @@ static int mca_be_hw_free(struct snd_pcm_substream *substream,
 	if (cl->port_driver < 0)
 		return -EINVAL;
 
+	/*
+	 * We are operating on a foreign cluster here, but since we
+	 * belong to the same PCM, accesses should have been
+	 * synchronized at ASoC level.
+	 */
 	fe_cl = &mca->clusters[cl->port_driver];
 	if (!mca_fe_clocks_in_use(fe_cl))
 		return 0; /* Nothing to do */
@@ -721,7 +734,9 @@ static int mca_be_startup(struct snd_pcm_substream *substream,
 		       cl->base + REG_PORT_CLOCK_SEL);
 	writel_relaxed(PORT_DATA_SEL_TXA(fe_cl->no),
 		       cl->base + REG_PORT_DATA_SEL);
+	mutex_lock(&mca->port_mutex);
 	cl->port_driver = fe_cl->no;
+	mutex_unlock(&mca->port_mutex);
 	cl->port_started[substream->stream] = true;
 
 	return 0;
@@ -731,6 +746,7 @@ static void mca_be_shutdown(struct snd_pcm_substream *substream,
 			    struct snd_soc_dai *dai)
 {
 	struct mca_cluster *cl = mca_dai_to_cluster(dai);
+	struct mca_data *mca = cl->host;
 
 	cl->port_started[substream->stream] = false;
 
@@ -741,7 +757,9 @@ static void mca_be_shutdown(struct snd_pcm_substream *substream,
 		 */
 		writel_relaxed(0, cl->base + REG_PORT_ENABLES);
 		writel_relaxed(0, cl->base + REG_PORT_DATA_SEL);
+		mutex_lock(&mca->port_mutex);
 		cl->port_driver = -1;
+		mutex_unlock(&mca->port_mutex);
 	}
 }
 
@@ -962,6 +980,7 @@ static int apple_mca_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	mca->dev = &pdev->dev;
 	mca->nclusters = nclusters;
+	mutex_init(&mca->port_mutex);
 	platform_set_drvdata(pdev, mca);
 	clusters = mca->clusters;