ASoC: stm32: dfsdm: manage multiple prepare

The DFSDM must be stopped when a new setting is applied.
restart systematically DFSDM on multiple prepare calls,
to apply changes.
Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/stm/stm32_adfsdm.c

@@ -9,6 +9,7 @@
 
 #include <linux/clk.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 
@@ -37,6 +38,8 @@ struct stm32_adfsdm_priv {
 	/* PCM buffer */
 	unsigned char *pcm_buff;
 	unsigned int pos;
+
+	struct mutex lock; /* protect against race condition on iio state */
 };
 
 static const struct snd_pcm_hardware stm32_adfsdm_pcm_hw = {
@@ -62,10 +65,12 @@ static void stm32_adfsdm_shutdown(struct snd_pcm_substream *substream,
 {
 	struct stm32_adfsdm_priv *priv = snd_soc_dai_get_drvdata(dai);
 
+	mutex_lock(&priv->lock);
 	if (priv->iio_active) {
 		iio_channel_stop_all_cb(priv->iio_cb);
 		priv->iio_active = false;
 	}
+	mutex_unlock(&priv->lock);
 }
 
 static int stm32_adfsdm_dai_prepare(struct snd_pcm_substream *substream,
@@ -74,13 +79,19 @@ static int stm32_adfsdm_dai_prepare(struct snd_pcm_substream *substream,
 	struct stm32_adfsdm_priv *priv = snd_soc_dai_get_drvdata(dai);
 	int ret;
 
+	mutex_lock(&priv->lock);
+	if (priv->iio_active) {
+		iio_channel_stop_all_cb(priv->iio_cb);
+		priv->iio_active = false;
+	}
+
 	ret = iio_write_channel_attribute(priv->iio_ch,
 					  substream->runtime->rate, 0,
 					  IIO_CHAN_INFO_SAMP_FREQ);
 	if (ret < 0) {
 		dev_err(dai->dev, "%s: Failed to set %d sampling rate\n",
 			__func__, substream->runtime->rate);
-		return ret;
+		goto out;
 	}
 
 	if (!priv->iio_active) {
@@ -92,6 +103,9 @@ static int stm32_adfsdm_dai_prepare(struct snd_pcm_substream *substream,
 				__func__, ret);
 	}
 
+out:
+	mutex_unlock(&priv->lock);
+
 	return ret;
 }
 
@@ -299,6 +313,7 @@ static int stm32_adfsdm_probe(struct platform_device *pdev)
 
 	priv->dev = &pdev->dev;
 	priv->dai_drv = stm32_adfsdm_dai;
+	mutex_init(&priv->lock);
 
 	dev_set_drvdata(&pdev->dev, priv);