[alsa-devel] [PATCH v3 3/6] soundwire: Add support to lock across bus instances

[Shreyas NC]

From: Sanyog Kale <sanyog.r.kale at intel.com>

Currently, the stream concept is limited to a Master and one or
more Codecs.

This patch extends the concept to support multiple Master(s)
sharing the same reference clock and synchronized in the hardware.
Modify sdw_stream_runtime to support a list of sdw_master_runtime
for the same. The existing reference to a single m_rt is removed
in the next patch.

Typically to lock, one would acquire a global lock and then lock
bus instances. In this case, the caller framework(ASoC DPCM)
guarantees that stream operations on a card are always serialized.
So, there is no race condition and hence no need for global lock.

Bus lock(s) are acquired to reconfigure the bus while the stream
is set-up.
So, we add sdw_acquire_bus_lock()/sdw_release_bus_lock() APIs which
are used only to reconfigure the bus.

Signed-off-by: Sanyog Kale <sanyog.r.kale at intel.com>
Signed-off-by: Vinod Koul <vkoul at kernel.org>
Signed-off-by: Shreyas NC <shreyas.nc at intel.com>
---
 drivers/soundwire/bus.h       |  2 ++
 drivers/soundwire/stream.c    | 41 +++++++++++++++++++++++++++++++++++++++++
 include/linux/soundwire/sdw.h |  4 ++++
 3 files changed, 47 insertions(+)

diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index 3b15c4e..b6cfbdf 100644
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -99,6 +99,7 @@ struct sdw_slave_runtime {
  * this stream, can be zero.
  * @slave_rt_list: Slave runtime list
  * @port_list: List of Master Ports configured for this stream, can be zero.
+ * @stream_node: sdw_stream_runtime master_list node
  * @bus_node: sdw_bus m_rt_list node
  */
 struct sdw_master_runtime {
@@ -108,6 +109,7 @@ struct sdw_master_runtime {
 	unsigned int ch_count;
 	struct list_head slave_rt_list;
 	struct list_head port_list;
+	struct list_head stream_node;
 	struct list_head bus_node;
 };
 
diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index 8974a0f..eb942c6 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -747,6 +747,7 @@ struct sdw_stream_runtime *sdw_alloc_stream(char *stream_name)
 		return NULL;
 
 	stream->name = stream_name;
+	INIT_LIST_HEAD(&stream->master_list);
 	stream->state = SDW_STREAM_ALLOCATED;
 
 	return stream;
@@ -1234,6 +1235,46 @@ struct sdw_dpn_prop *sdw_get_slave_dpn_prop(struct sdw_slave *slave,
 	return NULL;
 }
 
+/**
+ * sdw_acquire_bus_lock: Acquire bus lock for all Master runtime(s)
+ *
+ * @stream: SoundWire stream
+ *
+ * Acquire bus_lock for each of the master runtime(m_rt) part of this
+ * stream to reconfigure the bus.
+ */
+static void sdw_acquire_bus_lock(struct sdw_stream_runtime *stream)
+{
+	struct sdw_master_runtime *m_rt = NULL;
+	struct sdw_bus *bus = NULL;
+
+	/* Iterate for all Master(s) in Master list */
+	list_for_each_entry(m_rt, &stream->master_list, stream_node) {
+		bus = m_rt->bus;
+
+		mutex_lock(&bus->bus_lock);
+	}
+}
+
+/**
+ * sdw_release_bus_lock: Release bus lock for all Master runtime(s)
+ *
+ * @stream: SoundWire stream
+ *
+ * Release the previously held bus_lock after reconfiguring the bus.
+ */
+static void sdw_release_bus_lock(struct sdw_stream_runtime *stream)
+{
+	struct sdw_master_runtime *m_rt = NULL;
+	struct sdw_bus *bus = NULL;
+
+	/* Iterate for all Master(s) in Master list */
+	list_for_each_entry(m_rt, &stream->master_list, stream_node) {
+		bus = m_rt->bus;
+		mutex_unlock(&bus->bus_lock);
+	}
+}
+
 static int _sdw_prepare_stream(struct sdw_stream_runtime *stream)
 {
 	struct sdw_master_runtime *m_rt = stream->m_rt;
diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index 962971e..ccd8dcdf 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -769,6 +769,9 @@ struct sdw_stream_params {
  * @state: Current state of the stream
  * @type: Stream type PCM or PDM
  * @m_rt: Master runtime
+ * @master_list: List of Master runtime(s) in this stream.
+ * master_list can contain only one m_rt per Master instance
+ * for a stream
  */
 struct sdw_stream_runtime {
 	char *name;
@@ -776,6 +779,7 @@ struct sdw_stream_runtime {
 	enum sdw_stream_state state;
 	enum sdw_stream_type type;
 	struct sdw_master_runtime *m_rt;
+	struct list_head master_list;
 };
 
 struct sdw_stream_runtime *sdw_alloc_stream(char *stream_name);
-- 
2.7.4