linux-kernel - [PATCH 03/11] firmware: qcom-scm: atomically assign and read the global _

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Message-Id: <20230828192507.117334-4-bartosz.golaszewski@linaro.org>
Date:   Mon, 28 Aug 2023 21:24:59 +0200
From:   Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Alex Elder <elder@...aro.org>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     kernel@...cinc.com, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH 03/11] firmware: qcom-scm: atomically assign and read the global __scm pointer

Checking for the availability of SCM bridge can happen from any context.
It's only by chance that we haven't run into concurrency issues but with
the upcoming SHM Bridge driver that will be initiated at the same
initcall level, we need to assure the assignment and readback of the
__scm pointer is atomic.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/firmware/qcom_scm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
index 980fcfa20b9f..422de70faff8 100644
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -1331,7 +1331,7 @@ static int qcom_scm_find_dload_address(struct device *dev, u64 *addr)
  */
 bool qcom_scm_is_available(void)
 {
-	return !!__scm;
+	return !!READ_ONCE(__scm);
 }
 EXPORT_SYMBOL(qcom_scm_is_available);
 
@@ -1477,8 +1477,8 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	__scm = scm;
-	__scm->dev = &pdev->dev;
+	scm->dev = &pdev->dev;
+	WRITE_ONCE(__scm, scm);
 
 	init_completion(&__scm->waitq_comp);
 
-- 
2.39.2