[PATCH v2 5/5] soundwire: stream: Fix bandwidth leak in multi-link aggregation failure

[Bard Liao <yung-chuan.liao@linux.intel.com>]

From: David Lin <david.lin@intel.com>

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.

The rollback only restores bus->params, while the lane assignments of the
port runtimes are left untouched. Since _sdw_deprepare_stream() resets
p_rt->lane only when the lane's used bandwidth drops to zero, a stream can
also carry a stale lane from a previous prepare or from a failed prepare
that was rolled back. Reset the lane of the stream being prepared to 0 in
sdw_compute_bus_params() when no multi-lane is selected, so that the lane
assignment matches the restored lane_used_bandwidth.

Fixes: 7a30292ffa2a ("soundwire: generic_bandwidth_allocation: select data lane")
Cc: stable@vger.kernel.org
Signed-off-by: David Lin <david.lin@intel.com>
Co-developed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
---
 drivers/soundwire/bus.h                         |  3 +++
 .../soundwire/generic_bandwidth_allocation.c    | 14 ++++++++++++++
 drivers/soundwire/stream.c                      | 17 +++++++++++++----
 3 files changed, 30 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/generic_bandwidth_allocation.c b/drivers/soundwire/generic_bandwidth_allocation.c
index 9bacde2c67a1..214a1be6c33e 100644
--- a/drivers/soundwire/generic_bandwidth_allocation.c
+++ b/drivers/soundwire/generic_bandwidth_allocation.c
@@ -656,6 +656,20 @@ static int sdw_compute_bus_params(struct sdw_bus *bus,
 		list_for_each_entry(m_p_rt, &m_rt->port_list, port_node) {
 			m_p_rt->lane = m_lane;
 		}
+	} else if (prepare) {
+		/* Clear stale lane assignments when preparing on lane 0. */
+		list_for_each_entry(m_rt, &bus->m_rt_list, bus_node) {
+			if (m_rt->stream != stream)
+				continue;
+
+			list_for_each_entry(m_p_rt, &m_rt->port_list, port_node)
+				m_p_rt->lane = 0;
+
+			list_for_each_entry(s_rt, &m_rt->slave_rt_list, m_rt_node)
+				list_for_each_entry(s_p_rt, &s_rt->port_list, port_node)
+					s_p_rt->lane = 0;
+			break;
+		}
 	}
 
 	if (!mstr_prop->default_frame_rate || !mstr_prop->default_row)
diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index 06f051f03a21..7c748ba84767 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -1479,19 +1479,22 @@ 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) {
@@ -1542,7 +1545,13 @@ 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