linux-kernel - [PATCH v2 4/8] coresight: Add claim tag warnings and debug messages

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Message-Id: <20250318-james-coresight-claim-tags-v2-4-e9c8a9cde84e@linaro.org>
Date: Tue, 18 Mar 2025 16:21:58 +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 4/8] coresight: Add claim tag warnings and debug
 messages

Add a dev_dbg() message so that external debugger conflicts are more
visible. There are multiple reasons for -EBUSY so a message for this
particular one could be helpful. Add errors for and enumerate all the
other cases that are impossible.

Signed-off-by: James Clark <james.clark@...aro.org>
---
 drivers/hwtracing/coresight/coresight-core.c | 51 +++++++++++++++++-----------
 drivers/hwtracing/coresight/coresight-priv.h |  5 ++-
 2 files changed, 36 insertions(+), 20 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index e39043a9551f..5f08845faf0d 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -135,16 +135,6 @@ static inline u32 coresight_read_claim_tags(struct coresight_device *csdev)
 			 csdev_access_relaxed_read32(&csdev->access, CORESIGHT_CLAIMCLR));
 }
 
-static inline bool coresight_is_claimed_self_hosted(struct coresight_device *csdev)
-{
-	return coresight_read_claim_tags(csdev) == CORESIGHT_CLAIM_SELF_HOSTED;
-}
-
-static inline bool coresight_is_claimed_any(struct coresight_device *csdev)
-{
-	return coresight_read_claim_tags(csdev) != 0;
-}
-
 static inline void coresight_set_self_claim_tag(struct coresight_device *csdev)
 {
 	csdev_access_relaxed_write32(&csdev->access, CORESIGHT_CLAIM_SELF_HOSTED,
@@ -180,18 +170,41 @@ EXPORT_SYMBOL_GPL(coresight_clear_self_claim_tag_unlocked);
  */
 int coresight_claim_device_unlocked(struct coresight_device *csdev)
 {
+	int tag;
+	struct csdev_access *csa;
+
 	if (WARN_ON(!csdev))
 		return -EINVAL;
 
-	if (coresight_is_claimed_any(csdev))
+	csa = &csdev->access;
+	tag = coresight_read_claim_tags(csdev);
+
+	switch (tag) {
+	case CORESIGHT_CLAIM_FREE:
+		coresight_set_self_claim_tag(csdev);
+		if (coresight_read_claim_tags(csdev) == CORESIGHT_CLAIM_SELF_HOSTED)
+			return 0;
+
+		/* There was a race setting the tag, clean up and fail */
+		coresight_clear_self_claim_tag_unlocked(csa);
+		dev_dbg(&csdev->dev, "Busy: Couldn't set self claim tag");
 		return -EBUSY;
 
-	coresight_set_self_claim_tag(csdev);
-	if (coresight_is_claimed_self_hosted(csdev))
-		return 0;
-	/* There was a race setting the tag, clean up and fail */
-	coresight_clear_self_claim_tag_unlocked(&csdev->access);
-	return -EBUSY;
+	case CORESIGHT_CLAIM_EXTERNAL:
+		/* External debug is an expected state, so log and report BUSY */
+		dev_dbg(&csdev->dev, "Busy: Claimed by external debugger");
+		return -EBUSY;
+
+	default:
+	case CORESIGHT_CLAIM_SELF_HOSTED:
+	case CORESIGHT_CLAIM_INVALID:
+		/*
+		 * Warn here because we clear a lingering self hosted tag
+		 * on probe, so other tag combinations are impossible.
+		 */
+		dev_err_once(&csdev->dev, "Invalid claim tag state: %x", tag);
+		return -EBUSY;
+	}
 }
 EXPORT_SYMBOL_GPL(coresight_claim_device_unlocked);
 
@@ -220,7 +233,7 @@ void coresight_disclaim_device_unlocked(struct coresight_device *csdev)
 	if (WARN_ON(!csdev))
 		return;
 
-	if (coresight_is_claimed_self_hosted(csdev))
+	if (coresight_read_claim_tags(csdev) == CORESIGHT_CLAIM_SELF_HOSTED)
 		coresight_clear_self_claim_tag_unlocked(&csdev->access);
 	else
 		/*
@@ -228,7 +241,7 @@ void coresight_disclaim_device_unlocked(struct coresight_device *csdev)
 		 * and has manipulated it. Or something else has seriously
 		 * gone wrong in our driver.
 		 */
-		WARN_ON_ONCE(1);
+		dev_WARN_ONCE(&csdev->dev, 1, "External agent took claim tag");
 }
 EXPORT_SYMBOL_GPL(coresight_disclaim_device_unlocked);
 
diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
index 38bb4e8b50ef..6e8cf55aee0a 100644
--- a/drivers/hwtracing/coresight/coresight-priv.h
+++ b/drivers/hwtracing/coresight/coresight-priv.h
@@ -36,7 +36,10 @@ extern const struct device_type coresight_dev_type[];
  * 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 CORESIGHT_CLAIM_FREE		0
+#define CORESIGHT_CLAIM_EXTERNAL	1
+#define CORESIGHT_CLAIM_SELF_HOSTED	2
+#define CORESIGHT_CLAIM_INVALID		3
 
 #define TIMEOUT_US		100
 #define BMVAL(val, lsb, msb)	((val & GENMASK(msb, lsb)) >> lsb)

-- 
2.34.1