[PATCH 2/2] soundwire: stream: Fix bandwidth leak in multi-link aggregation failure

[Bard Liao]

From: David Lin <david.lin@xxxxxxxxx>

When preparing a multi-link aggregation stream, a failure on a subsequent
link during _sdw_prepare_stream() causes the stream preparation to fail.
However, the bandwidth allocated on the preceding successful links is never
released, causing a cumulative bandwidth leak.

Fix this by saving a snapshot of each bus's parameters before making any
modifications. In case of failure, we iterate through the stream's master
list and restore each bus to its original parameter state, ensuring an
atomic rollback and preventing any bandwidth leaks.

Signed-off-by: David Lin <david.lin@xxxxxxxxx>
Co-developed-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
Signed-off-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@xxxxxxxxxxxxxxx>
---
 drivers/soundwire/bus.h    |  3 +++
 drivers/soundwire/stream.c | 17 +++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index 44e4f5193917..476387b70472 100644
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -155,6 +155,8 @@ struct sdw_slave_runtime {
  *
  * @bus: Bus handle
  * @stream: Stream runtime handle
+ * @params_backup: Snapshot of original bus parameters saved before stream
+ * preparation, used for rollback recovery on failure.
  * @direction: Data direction for Master
  * @ch_count: Number of channels handled by the Master for
  * this stream, can be zero.
@@ -166,6 +168,7 @@ struct sdw_slave_runtime {
 struct sdw_master_runtime {
 	struct sdw_bus *bus;
 	struct sdw_stream_runtime *stream;
+	struct sdw_bus_params params_backup;
 	enum sdw_data_direction direction;
 	unsigned int ch_count;
 	struct list_head slave_rt_list;
diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index 96613dd0677c..86d951cc92f7 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -1477,19 +1477,22 @@ static int _sdw_prepare_stream(struct sdw_stream_runtime *stream,
 	struct sdw_master_runtime *m_rt;
 	struct sdw_bus *bus;
 	struct sdw_master_prop *prop;
-	struct sdw_bus_params params;
 	int ret;
 
+	/* Pre-pass: snapshot original bus parameters for all masters */
+	list_for_each_entry(m_rt, &stream->master_list, stream_node)
+		m_rt->params_backup = m_rt->bus->params;
+
 	/* Prepare  Master(s) and Slave(s) port(s) associated with stream */
 	list_for_each_entry(m_rt, &stream->master_list, stream_node) {
 		bus = m_rt->bus;
 		prop = &bus->prop;
-		memcpy(&params, &bus->params, sizeof(params));
 
 		/* TODO: Support Asynchronous mode */
 		if ((prop->max_clk_freq % stream->params.rate) != 0) {
 			dev_err(bus->dev, "Async mode not supported\n");
-			return -EINVAL;
+			ret = -EINVAL;
+			goto restore_params;
 		}
 
 		if (update_params) {
@@ -1540,7 +1543,13 @@ static int _sdw_prepare_stream(struct sdw_stream_runtime *stream,
 	return ret;
 
 restore_params:
-	memcpy(&bus->params, &params, sizeof(params));
+	/*
+	 * Revert all masters to their snapshotted original parameters.
+	 * Any master that was not modified will safely revert to its own original state.
+	 */
+	list_for_each_entry(m_rt, &stream->master_list, stream_node)
+		m_rt->bus->params = m_rt->params_backup;
+
 	return ret;
 }
 
-- 
2.43.0