[alsa-devel] [PATCH v3 13/22] soundwire: bus: fix race condition with initialization_complete signaling

[Pierre-Louis Bossart]

Waiting for the enumeration to be complete may not be enough for a
Slave driver, there is a possible race condition between resume
operations and initializations handled in an interrupt thread, which
can results in settings not being fully restored after system or
pm_runtime resume.

This patch builds on the changes added for enumeration_complete,
init_completion() is called when the Slave device becomes UNATTACHED,
as done with enumeration_complete.

The difference with the enumeration_complete case is that complete()
is signaled after the Slave device is fully initialized after the
.update_status() callback is called.

A Slave device driver can decide to wait on either of the two
complete() cases, depending on its initialization code and
requirements.

Signed-off-by: Rander Wang <rander.wang at linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
---
 drivers/soundwire/bus.c   | 8 ++++++++
 drivers/soundwire/slave.c | 1 +
 2 files changed, 9 insertions(+)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index e34b5ed534b3..329f35a40649 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -648,6 +648,7 @@ static void sdw_modify_slave_status(struct sdw_slave *slave,
 			__func__, slave->dev_num);
 
 		init_completion(&slave->enumeration_complete);
+		init_completion(&slave->initialization_complete);
 
 	} else if (status == SDW_SLAVE_ATTACHED) {
 		dev_dbg(&slave->dev,
@@ -1051,6 +1052,7 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 {
 	enum sdw_slave_status prev_status;
 	struct sdw_slave *slave;
+	bool attached_initializing;
 	int i, ret = 0;
 
 	/* first check if any Slaves fell off the bus */
@@ -1096,6 +1098,8 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 		if (!slave)
 			continue;
 
+		attached_initializing = false;
+
 		switch (status[i]) {
 		case SDW_SLAVE_UNATTACHED:
 			if (slave->status == SDW_SLAVE_UNATTACHED)
@@ -1122,6 +1126,8 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 			if (prev_status == SDW_SLAVE_ALERT)
 				break;
 
+			attached_initializing = true;
+
 			ret = sdw_initialize_slave(slave);
 			if (ret)
 				dev_err(bus->dev,
@@ -1140,6 +1146,8 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 		if (ret)
 			dev_err(slave->bus->dev,
 				"Update Slave status failed:%d\n", ret);
+		if (attached_initializing)
+			complete(&slave->initialization_complete);
 	}
 
 	return ret;
diff --git a/drivers/soundwire/slave.c b/drivers/soundwire/slave.c
index 76fdfbd8b50d..d2a952d9bd47 100644
--- a/drivers/soundwire/slave.c
+++ b/drivers/soundwire/slave.c
@@ -53,6 +53,7 @@ static int sdw_slave_add(struct sdw_bus *bus,
 	slave->bus = bus;
 	slave->status = SDW_SLAVE_UNATTACHED;
 	init_completion(&slave->enumeration_complete);
+	init_completion(&slave->initialization_complete);
 	slave->dev_num = 0;
 	init_completion(&slave->probe_complete);
 	slave->probed = false;
-- 
2.20.1