[alsa-devel] [PATCH 06/10] soundwire: bus: add helper to clear Slave status to UNATTACHED

[Pierre-Louis Bossart]

When resuming with a bus reset, we need to re-enumerate and restart
from UNATTACHED. The helper added in this patch helps implement a more
robust state machine avoiding race conditions on resume.

The unattach request is stored and will be used by Slave drivers, if
needed: Intel validation exposed a corner case where the Slave device
may transition to D3 when streaming stops, but streaming restarts
before the Master transitions to D3. In that case, the Slave status
was not cleared as UNATTACHED by the Master resuming, and the
wait_for_completion will time out.

When the slave resumes, it can check if a Master-initiated
re-enumeration and initialization took place and skip the
wait_for_completion() if there is no reason to wait.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
---
 drivers/soundwire/bus.c | 27 +++++++++++++++++++++++++++
 drivers/soundwire/bus.h |  8 ++++++++
 2 files changed, 35 insertions(+)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index dfe27e3ca815..57dec61142e5 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -1163,3 +1163,30 @@ int sdw_handle_slave_status(struct sdw_bus *bus,
 	return ret;
 }
 EXPORT_SYMBOL(sdw_handle_slave_status);
+
+void sdw_clear_slave_status(struct sdw_bus *bus, u32 request)
+{
+	struct sdw_slave *slave;
+	int i;
+
+	/* Check all non-zero devices */
+	for (i = 1; i <= SDW_MAX_DEVICES; i++) {
+		mutex_lock(&bus->bus_lock);
+		if (test_bit(i, bus->assigned) == false) {
+			mutex_unlock(&bus->bus_lock);
+			continue;
+		}
+		mutex_unlock(&bus->bus_lock);
+
+		slave = sdw_get_slave(bus, i);
+		if (!slave)
+			continue;
+
+		if (slave->status != SDW_SLAVE_UNATTACHED)
+			sdw_modify_slave_status(slave, SDW_SLAVE_UNATTACHED);
+
+		/* keep track of request, used in pm_runtime resume */
+		slave->unattach_request = request;
+	}
+}
+EXPORT_SYMBOL(sdw_clear_slave_status);
diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index acb8d11a4c84..204204a26db8 100644
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -165,4 +165,12 @@ sdw_update(struct sdw_slave *slave, u32 addr, u8 mask, u8 val)
 	return sdw_write(slave, addr, tmp);
 }
 
+/*
+ * At the moment we only track Master-initiated hw_reset.
+ * Additional fields can be added as needed
+ */
+#define SDW_UNATTACH_REQUEST_MASTER_RESET	BIT(0)
+
+void sdw_clear_slave_status(struct sdw_bus *bus, u32 request);
+
 #endif /* __SDW_BUS_H */
-- 
2.20.1