Fix restore_params to restore all buses in multi-link streams

The restore_params block in _sdw_prepare_stream() was restoring only
the last bus iterated when an error occurred. For multi-link streams
with multiple buses, this left other buses in a partially reconfigured
state.

Fix this by:
1. Adding bpt_hstop to sdw_bus to track the BPT stream hstop value.
2. Adding saved_params and saved_bpt_hstop to sdw_master_runtime to
   store per-bus backup state.
3. Pre-saving all buses' params and bpt_hstop before the modify loop.
4. Restoring all buses from their per-bus saved state in restore_params.

Addresses review comment: #5604 (comment)

Author: Copilot

drivers/soundwire/bus.h

@@ -172,6 +172,8 @@ struct sdw_master_runtime {
 	struct list_head port_list;
 	struct list_head stream_node;
 	struct list_head bus_node;
+	struct sdw_bus_params saved_params;
+	int saved_bpt_hstop;
 };
 
 struct sdw_transport_data {

drivers/soundwire/stream.c

@@ -1479,14 +1479,19 @@ 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-save all buses' params before making any changes, for error recovery */
+	list_for_each_entry(m_rt, &stream->master_list, stream_node) {
+		bus = m_rt->bus;
+		memcpy(&m_rt->saved_params, &bus->params, sizeof(bus->params));
+		m_rt->saved_bpt_hstop = bus->bpt_hstop;
+	}
+
 	/* 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) {
@@ -1542,7 +1547,11 @@ static int _sdw_prepare_stream(struct sdw_stream_runtime *stream,
 	return ret;
 
 restore_params:
-	memcpy(&bus->params, &params, sizeof(params));
+	list_for_each_entry(m_rt, &stream->master_list, stream_node) {
+		bus = m_rt->bus;
+		memcpy(&bus->params, &m_rt->saved_params, sizeof(bus->params));
+		bus->bpt_hstop = m_rt->saved_bpt_hstop;
+	}
 	return ret;
 }
 

include/linux/soundwire/sdw.h

@@ -1003,6 +1003,7 @@ struct sdw_stream_runtime {
  * @stream_refcount: number of streams currently using this bus
  * @bpt_stream_refcount: number of BTP streams currently using this bus (should
  * be zero or one, multiple streams per link is not supported).
+ * @bpt_hstop: The hstop of the BPT stream.
  * @bpt_stream: pointer stored to handle BTP streams.
  * @ops: Master callback ops
  * @port_ops: Master port callback ops
@@ -1043,6 +1044,7 @@ struct sdw_bus {
 	struct sdw_bus_params params;
 	int stream_refcount;
 	int bpt_stream_refcount;
+	int bpt_hstop;
 	struct sdw_stream_runtime *bpt_stream;
 	const struct sdw_master_ops *ops;
 	const struct sdw_master_port_ops *port_ops;