ASoC: SOF: fix PCM playback through ALSA OSS emulation

Any app using ALSA OSS emulation on top of SOF will fail
to error from OSS SNDCTL_DSP_SETFMT ioctl. Reported initially
as an issue with xournalpp (application using PortAudio with
an OSS backend), but applies more generally to other apps
using OSS as well.

Problem is caused by SOF PCM not supporting repeated calls
to hw_params(), without matching calls to pcm_free(). This
is however exactly what the ALSA OSS PCM code is doing when
it is handling the OSS ioctls.

The problem will lead to leaking of DSP resources and eventual
failure of DSP PCM_PARAMS IPC.

BugLink: #1510
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

sound/soc/sof/pcm.c

@@ -92,6 +92,27 @@ void snd_sof_pcm_period_elapsed(struct snd_pcm_substream *substream)
 }
 EXPORT_SYMBOL(snd_sof_pcm_period_elapsed);
 
+static int sof_pcm_dsp_pcm_free(struct snd_pcm_substream *substream,
+				struct snd_sof_dev *sdev,
+				struct snd_sof_pcm *spcm)
+{
+	struct sof_ipc_stream stream;
+	struct sof_ipc_reply reply;
+	int ret;
+
+	stream.hdr.size = sizeof(stream);
+	stream.hdr.cmd = SOF_IPC_GLB_STREAM_MSG | SOF_IPC_STREAM_PCM_FREE;
+	stream.comp_id = spcm->stream[substream->stream].comp_id;
+
+	/* send IPC to the DSP */
+	ret = sof_ipc_tx_message(sdev->ipc, stream.hdr.cmd, &stream,
+				 sizeof(stream), &reply, sizeof(reply));
+	if (!ret)
+		spcm->prepared[substream->stream] = false;
+
+	return ret;
+}
+
 /* this may get called several times by oss emulation */
 static int sof_pcm_hw_params(struct snd_soc_component *component,
 			     struct snd_pcm_substream *substream,
@@ -113,6 +134,16 @@ static int sof_pcm_hw_params(struct snd_soc_component *component,
 	if (!spcm)
 		return -EINVAL;
 
+	/*
+	 * Handle repeated calls to hw_params() without free_pcm() in
+	 * between. At least ALSA OSS emulation depends on this.
+	 */
+	if (spcm->prepared[substream->stream]) {
+		ret = sof_pcm_dsp_pcm_free(substream, sdev, spcm);
+		if (ret < 0)
+			return ret;
+	}
+
 	dev_dbg(component->dev, "pcm: hw params stream %d dir %d\n",
 		spcm->pcm.pcm_id, substream->stream);
 
@@ -201,27 +232,6 @@ static int sof_pcm_hw_params(struct snd_soc_component *component,
 	return ret;
 }
 
-static int sof_pcm_dsp_pcm_free(struct snd_pcm_substream *substream,
-				struct snd_sof_dev *sdev,
-				struct snd_sof_pcm *spcm)
-{
-	struct sof_ipc_stream stream;
-	struct sof_ipc_reply reply;
-	int ret;
-
-	stream.hdr.size = sizeof(stream);
-	stream.hdr.cmd = SOF_IPC_GLB_STREAM_MSG | SOF_IPC_STREAM_PCM_FREE;
-	stream.comp_id = spcm->stream[substream->stream].comp_id;
-
-	/* send IPC to the DSP */
-	ret = sof_ipc_tx_message(sdev->ipc, stream.hdr.cmd, &stream,
-				 sizeof(stream), &reply, sizeof(reply));
-	if (!ret)
-		spcm->prepared[substream->stream] = false;
-
-	return ret;
-}
-
 static int sof_pcm_hw_free(struct snd_soc_component *component,
 			   struct snd_pcm_substream *substream)
 {