linux-kernel - [PATCH 1/1] coresight: fix issue where coresight component has no claimtags

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Message-Id: <20251021234520.3355-2-mike.leach@linaro.org>
Date: Wed, 22 Oct 2025 00:45:20 +0100
From: Mike Leach <mike.leach@...aro.org>
To: coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: suzuki.poulose@....com,
	leo.yan@....com,
	james.clark@...aro.org,
	Mike Leach <mike.leach@...aro.org>
Subject: [PATCH 1/1] coresight: fix issue where coresight component has no claimtags

Coresight components have 0 to 8 claim tag bits. ARM recommends 4 and
the implemented claim tag protocol uses two of these.

If a component has insufficient claim tags then the protocol incorrectly
returns an error when attempting to claim a component.

Fix by reading CLAIMSET to establish then actual number of claim tags
and return success when attempting to claim a component were there are
insufficient tags to implement the protocol.

Signed-off-by: Mike Leach <mike.leach@...aro.org>
---
 drivers/hwtracing/coresight/coresight-core.c | 26 ++++++++++++++++++++
 drivers/hwtracing/coresight/coresight-priv.h |  8 ++++++
 2 files changed, 34 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 3267192f0c1c..ce4eade8a1e3 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -131,6 +131,22 @@ coresight_find_out_connection(struct coresight_device *csdev,
 	return ERR_PTR(-ENODEV);
 }
 
+/*
+ * Reading CLIAMSET returns  a bitfield representing the number of claim tags
+ * implemented from bit 0 to bit nTag-1, valid bits set to 1.
+ *
+ * Claim protocol requires 2 bits so test for highest bit required,
+ * bit 1 -  CORESIGHT_CLAIM_SELF_HOSTED_BIT
+ *
+ * return true if sufficient claim tags implemented for protocol
+ */
+static bool coresight_claim_tags_implemented_unlocked(struct csdev_access *csa)
+{
+	u32 claim_bits_impl = FIELD_GET(CORESIGHT_CLAIM_BITS_MAX_MASK,
+			 csdev_access_relaxed_read32(csa, CORESIGHT_CLAIMSET));
+	return ((claim_bits_impl & CORESIGHT_CLAIM_SELF_HOSTED_BIT) != 0);
+}
+
 static u32 coresight_read_claim_tags_unlocked(struct coresight_device *csdev)
 {
 	return FIELD_GET(CORESIGHT_CLAIM_MASK,
@@ -156,6 +172,9 @@ EXPORT_SYMBOL_GPL(coresight_clear_self_claim_tag);
 
 void coresight_clear_self_claim_tag_unlocked(struct csdev_access *csa)
 {
+	if (!coresight_claim_tags_implemented_unlocked(csa))
+		return;
+
 	csdev_access_relaxed_write32(csa, CORESIGHT_CLAIM_SELF_HOSTED,
 				     CORESIGHT_CLAIMCLR);
 	isb();
@@ -181,6 +200,10 @@ int coresight_claim_device_unlocked(struct coresight_device *csdev)
 		return -EINVAL;
 
 	csa = &csdev->access;
+
+	if (!coresight_claim_tags_implemented_unlocked(csa))
+		return 0;
+
 	tag = coresight_read_claim_tags_unlocked(csdev);
 
 	switch (tag) {
@@ -237,6 +260,9 @@ void coresight_disclaim_device_unlocked(struct coresight_device *csdev)
 	if (WARN_ON(!csdev))
 		return;
 
+	if (!coresight_claim_tags_implemented_unlocked(&csdev->access))
+		return;
+
 	if (coresight_read_claim_tags_unlocked(csdev) == CORESIGHT_CLAIM_SELF_HOSTED)
 		coresight_clear_self_claim_tag_unlocked(&csdev->access);
 	else
diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
index 33e22b1ba043..f93cbc9bb36a 100644
--- a/drivers/hwtracing/coresight/coresight-priv.h
+++ b/drivers/hwtracing/coresight/coresight-priv.h
@@ -41,6 +41,14 @@ extern const struct device_type coresight_dev_type[];
 #define CORESIGHT_CLAIM_SELF_HOSTED	2
 #define CORESIGHT_CLAIM_INVALID		3
 
+/*
+ * Coresight specification defines a maximum of 8 claim tag bits.
+ * The precise number is implementation defined, and may be obtained by
+ * reading the CLAIMSET register.
+ */
+#define CORESIGHT_CLAIM_BITS_MAX_MASK	GENMASK(7, 0)
+#define CORESIGHT_CLAIM_SELF_HOSTED_BIT	BIT(1)
+
 #define TIMEOUT_US		100
 #define BMVAL(val, lsb, msb)	((val & GENMASK(msb, lsb)) >> lsb)
 
-- 
2.32.0