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@arm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250325-james-coresight-claim-tags-v4-2-dfbd3822b2e5@linaro.org

Author: james-c-linaro

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_unlocked(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)

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