[PATCH 5/6] soudnwire: master: protect concurrecnt check for bus->md

[Krzysztof Kozlowski]

The Soundwire master controllers might want to check for bus->md
initialization to avoid race between early interrupt and finish of
sdw_bus_master_add()/sdw_master_device_add().  Such early interrupt can
happen if Soundwire devices are not powered off during their probe.

Add a store release barrier, so the Soundwire controllers can safely
check it in concurrent (e.g. in interrupt) way.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>

---

Cc: Patrick Lai <quic_plai@xxxxxxxxxxx>
---
 drivers/soundwire/master.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/master.c b/drivers/soundwire/master.c
index 9b05c9e25ebe..d5bf13e7e602 100644
--- a/drivers/soundwire/master.c
+++ b/drivers/soundwire/master.c
@@ -161,7 +161,12 @@ int sdw_master_device_add(struct sdw_bus *bus, struct device *parent,
 	/* add shortcuts to improve code readability/compactness */
 	md->bus = bus;
 	bus->dev = &md->dev;
-	bus->md = md;
+	/*
+	 * Make sure the contents of md is stored before storing bus->md.
+	 * Paired with new slave attached and slave status interrupts
+	 * on the Soundwire master side.
+	 */
+	smp_store_release(&bus->md, md);
 
 	pm_runtime_set_autosuspend_delay(&bus->md->dev, SDW_MASTER_SUSPEND_DELAY_MS);
 	pm_runtime_use_autosuspend(&bus->md->dev);
-- 
2.34.1