linux-kernel - [PATCH 3/7] coresight: Only check bottom two claim bits

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Message-Id: <20250211103945.967495-4-james.clark@linaro.org>
Date: Tue, 11 Feb 2025 10:39:39 +0000
From: James Clark <james.clark@...aro.org>
To: lcherian@...vell.com,
	coresight@...ts.linaro.org
Cc: James Clark <james.clark@...aro.org>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com
Subject: [PATCH 3/7] coresight: Only check bottom two claim bits

The use of the whole register and == could break the claim mechanism if
any of the other bits are used in the future. The referenced doc "PSCI -
ARM DEN 0022D" also says to only read and clear the bottom two bits.

Use FIELD_GET() to extract only the relevant part.

Signed-off-by: James Clark <james.clark@...aro.org>
---
 drivers/hwtracing/coresight/coresight-core.c | 3 ++-
 drivers/hwtracing/coresight/coresight-priv.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index a669872b4118..7b53165c93af 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -129,7 +129,8 @@ coresight_find_out_connection(struct coresight_device *csdev,
 
 static inline u32 coresight_read_claim_tags(struct csdev_access *csa)
 {
-	return csdev_access_relaxed_read32(csa, CORESIGHT_CLAIMCLR);
+	return FIELD_GET(CORESIGHT_CLAIM_MASK,
+			 csdev_access_relaxed_read32(csa, CORESIGHT_CLAIMCLR));
 }
 
 static inline bool coresight_is_claimed_self_hosted(struct csdev_access *csa)
diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
index 05f891ca6b5c..cc7ff1e36ef4 100644
--- a/drivers/hwtracing/coresight/coresight-priv.h
+++ b/drivers/hwtracing/coresight/coresight-priv.h
@@ -35,6 +35,7 @@ extern const struct device_type coresight_dev_type[];
  * Coresight device CLAIM protocol.
  * See PSCI - ARM DEN 0022D, Section: 6.8.1 Debug and Trace save and restore.
  */
+#define CORESIGHT_CLAIM_MASK		GENMASK(1, 0)
 #define CORESIGHT_CLAIM_SELF_HOSTED	BIT(1)
 
 #define TIMEOUT_US		100
-- 
2.34.1