ASoC: sh: rz-ssi: Add rz_ssi_set_substream() helper function

A copy of substream pointer is stored in priv structure during
rz_ssi_dai_trigger() callback ie in SNDRV_PCM_TRIGGER_START case
and the pointer is assigned to NULL in case of SNDRV_PCM_TRIGGER_STOP.

The driver used the locks only in rz_ssi_stream_is_valid() and assigned
the local substream pointer to NULL in rz_ssi_dai_trigger() callback but
never locked it while making a local copy.

This patch adds the rz_ssi_set_substream() helper function to set the
substream pointer with locks acquired and replaces the instances of
setting the local substream pointer with the rz_ssi_set_substream()
function.
Reported-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20220125132457.14984-3-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rz-ssi.c

@@ -188,6 +188,17 @@ static inline bool rz_ssi_is_dma_enabled(struct rz_ssi_priv *ssi)
 	return (ssi->playback.dma_ch && (ssi->dma_rt || ssi->capture.dma_ch));
 }
 
+static void rz_ssi_set_substream(struct rz_ssi_stream *strm,
+				 struct snd_pcm_substream *substream)
+{
+	struct rz_ssi_priv *ssi = strm->priv;
+	unsigned long flags;
+
+	spin_lock_irqsave(&ssi->lock, flags);
+	strm->substream = substream;
+	spin_unlock_irqrestore(&ssi->lock, flags);
+}
+
 static bool rz_ssi_stream_is_valid(struct rz_ssi_priv *ssi,
 				   struct rz_ssi_stream *strm)
 {
@@ -206,7 +217,7 @@ static void rz_ssi_stream_init(struct rz_ssi_stream *strm,
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 
-	strm->substream = substream;
+	rz_ssi_set_substream(strm, substream);
 	strm->sample_width = samples_to_bytes(runtime, 1);
 	strm->dma_buffer_pos = 0;
 	strm->period_counter = 0;
@@ -224,11 +235,8 @@ static void rz_ssi_stream_quit(struct rz_ssi_priv *ssi,
 			       struct rz_ssi_stream *strm)
 {
 	struct snd_soc_dai *dai = rz_ssi_get_dai(strm->substream);
-	unsigned long flags;
 
-	spin_lock_irqsave(&ssi->lock, flags);
-	strm->substream = NULL;
-	spin_unlock_irqrestore(&ssi->lock, flags);
+	rz_ssi_set_substream(strm, NULL);
 
 	if (strm->oerr_num > 0)
 		dev_info(dai->dev, "overrun = %d\n", strm->oerr_num);