[PATCH v2 1/1] coresight: fix issue where coresight component has no claimtags

[Mike Leach <mike.leach@linaro.org>]

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@linaro.org>
---
 drivers/hwtracing/coresight/coresight-core.c | 46 ++++++++++++++++++--
 drivers/hwtracing/coresight/coresight-priv.h | 10 +++++
 include/linux/coresight.h                    | 15 +++++++
 3 files changed, 68 insertions(+), 3 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 3267192f0c1c..61b4902b0ead 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -131,6 +131,39 @@ coresight_find_out_connection(struct coresight_device *csdev,
 	return ERR_PTR(-ENODEV);
 }
 
+/*
+ * Reading CLAiMSET 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 MS bit required,
+ * bit 1 -  CORESIGHT_CLAIM_BIT_PROTOCOL_HI
+ *
+ * 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_BIT_PROTOCOL_HI) != 0);
+}
+
+/*
+ * check if we can use the claim tag protocol.
+ *
+ * If currently unknown - read register to determine if sufficient tags and
+ * save value, otherwise return current value.
+ */
+static bool coresight_check_use_claim_tag_unlocked(struct coresight_device *csdev)
+{
+	if (csdev->claim_tag_info == CS_CLAIM_TAG_UNKNOWN) {
+		if (coresight_claim_tags_implemented_unlocked(&csdev->access))
+			csdev->claim_tag_info = CS_CLAIM_TAG_STD_PROTOCOL;
+		else
+			csdev->claim_tag_info = CS_CLAIM_TAG_NOT_IMPL;
+	}
+	return (csdev->claim_tag_info == CS_CLAIM_TAG_STD_PROTOCOL);
+}
+
 static u32 coresight_read_claim_tags_unlocked(struct coresight_device *csdev)
 {
 	return FIELD_GET(CORESIGHT_CLAIM_MASK,
@@ -156,6 +189,9 @@ 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();
@@ -175,12 +211,13 @@ 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;
 
-	csa = &csdev->access;
+	if (!coresight_check_use_claim_tag_unlocked(csdev))
+		return 0;
+
 	tag = coresight_read_claim_tags_unlocked(csdev);
 
 	switch (tag) {
@@ -190,7 +227,7 @@ int coresight_claim_device_unlocked(struct coresight_device *csdev)
 			return 0;
 
 		/* There was a race setting the tag, clean up and fail */
-		coresight_clear_self_claim_tag_unlocked(csa);
+		coresight_clear_self_claim_tag_unlocked(&csdev->access);
 		dev_dbg(&csdev->dev, "Busy: Couldn't set self claim tag");
 		return -EBUSY;
 
@@ -237,6 +274,9 @@ void coresight_disclaim_device_unlocked(struct coresight_device *csdev)
 	if (WARN_ON(!csdev))
 		return;
 
+	if (!coresight_check_use_claim_tag_unlocked(csdev))
+		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..270f179c8535 100644
--- a/drivers/hwtracing/coresight/coresight-priv.h
+++ b/drivers/hwtracing/coresight/coresight-priv.h
@@ -41,6 +41,16 @@ 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)
+
+/* MS Bit required by the protocol */
+#define CORESIGHT_CLAIM_BIT_PROTOCOL_HI	BIT(1)
+
 #define TIMEOUT_US		100
 #define BMVAL(val, lsb, msb)	((val & GENMASK(msb, lsb)) >> lsb)
 
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 6de59ce8ef8c..fefe4317a793 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -242,6 +242,19 @@ struct coresight_trace_id_map {
 	raw_spinlock_t lock;
 };
 
+/*
+ * Coresight claim tag info:
+ * CS_CLAIM_TAG_UNKNOWN      - not yet checked.
+ * CS_CLAIM_TAG_STD_PROTOCOL - using standard claim/release protocol.
+ * CS_CLAIM_TAG_NOT_IMPL     - no claim tags available.
+ */
+enum coresight_claim_tag_info {
+	CS_CLAIM_TAG_UNKNOWN,
+	CS_CLAIM_TAG_STD_PROTOCOL,
+	CS_CLAIM_TAG_NOT_IMPL,
+};
+
+
 /**
  * struct coresight_device - representation of a device as used by the framework
  * @pdata:	Platform data with device connections associated to this device.
@@ -265,6 +278,7 @@ struct coresight_trace_id_map {
  *		CS_MODE_SYSFS. Otherwise it must be accessed from inside the
  *		spinlock.
  * @orphan:	true if the component has connections that haven't been linked.
+ * @claim_tag_info: how the device is using claim tags.
  * @sysfs_sink_activated: 'true' when a sink has been selected for use via sysfs
  *		by writing a 1 to the 'enable_sink' file.  A sink can be
  *		activated but not yet enabled.  Enabling for a _sink_ happens
@@ -291,6 +305,7 @@ struct coresight_device {
 	local_t	mode;
 	int refcnt;
 	bool orphan;
+	enum coresight_claim_tag_info claim_tag_info;
 	/* sink specific fields */
 	bool sysfs_sink_activated;
 	struct dev_ext_attribute *ea;
-- 
2.32.0