linux-kernel - [PATCH v2 3/8] coresight: Only check bottom two claim bits

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Message-Id: <20250318-james-coresight-claim-tags-v2-3-e9c8a9cde84e@linaro.org>
Date: Tue, 18 Mar 2025 16:21:57 +0000
From: James Clark <james.clark@...aro.org>
To: Suzuki K Poulose <suzuki.poulose@....com>, 
 Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>, 
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
 Maxime Coquelin <mcoquelin.stm32@...il.com>, 
 Alexandre Torgue <alexandre.torgue@...s.st.com>, Suzuki.Poulose@....com, 
 leo.yan@....com
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com
Subject: [PATCH v2 3/8] 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.

Reviewed-by: Leo Yan <leo.yan@....com>
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 9ff601e2415a..e39043a9551f 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -131,7 +131,8 @@ coresight_find_out_connection(struct coresight_device *csdev,
 
 static inline u32 coresight_read_claim_tags(struct coresight_device *csdev)
 {
-	return csdev_access_relaxed_read32(&csdev->access, CORESIGHT_CLAIMCLR);
+	return FIELD_GET(CORESIGHT_CLAIM_MASK,
+			 csdev_access_relaxed_read32(&csdev->access, CORESIGHT_CLAIMCLR));
 }
 
 static inline bool coresight_is_claimed_self_hosted(struct coresight_device *csdev)
diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
index 82644aff8d2b..38bb4e8b50ef 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