soundwire: stream: only prepare stream when it is configured.

We don't need to prepare the stream again if the stream is already
prepared.

sdw_prepare_stream() could be called multiple times without calling
sdw_deprepare_stream(). We call sdw_prepare_stream() in the prepare
dai ops and sdw_deprepare_stream() in the hw_free dai ops. If an xrun
happens, sdw_prepare_stream() will be called but
sdw_deprepare_stream() will not, which results in an imbalance and an
invalid total bandwidth.
Signed-off-by: NPierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: NBard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20200114235227.14502-3-pierre-louis.bossart@linux.intel.comSigned-off-by: NVinod Koul <vkoul@kernel.org>

drivers/soundwire/stream.c

@@ -1544,7 +1544,7 @@ static int _sdw_prepare_stream(struct sdw_stream_runtime *stream)
  */
 int sdw_prepare_stream(struct sdw_stream_runtime *stream)
 {
-	int ret = 0;
+	int ret;
 
 	if (!stream) {
 		pr_err("SoundWire: Handle not found for stream\n");
@@ -1553,6 +1553,11 @@ int sdw_prepare_stream(struct sdw_stream_runtime *stream)
 
 	sdw_acquire_bus_lock(stream);
 
+	if (stream->state == SDW_STREAM_PREPARED) {
+		ret = 0;
+		goto state_err;
+	}
+
 	if (stream->state != SDW_STREAM_CONFIGURED &&
 	    stream->state != SDW_STREAM_DEPREPARED &&
 	    stream->state != SDW_STREAM_DISABLED) {