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

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Date:   Thu, 20 Apr 2023 12:16:16 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Vinod Koul <vkoul@...nel.org>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Patrick Lai <quic_plai@...cinc.com>
Subject: [PATCH 5/6] soudnwire: master: protect concurrecnt check for bus->md

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@...aro.org>

---

Cc: Patrick Lai <quic_plai@...cinc.com>
---
 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