linux-kernel - [PATCH v2 0/1] coresight: fix issue with insufficient claim tags

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Message-Id: <20251027223545.2801-1-mike.leach@linaro.org>
Date: Mon, 27 Oct 2025 22:35:44 +0000
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 v2 0/1] coresight: fix issue with insufficient claim tags

All CoreSight compliant components have an implementation defined number
of 0 to 8 claim tag bits in the claim tag registers.

These are used to claim the CoreSight resources by system agents.

ARM recommends implementions have 4 claim tag registers.

The CoreSight drivers implement a 2 claim tag bit protocol to allow
self hosted and external debug agents to manage access to the hardware.

However, if there are less than 2 claim tags available the protocol
incorrectly returns an error on device claim, as no checks are made.

If insufficient claim tags are present in a component then the protocol
must return success on claim / disclaim to allow components to be used
normally.

Changes read the CLAIMSET bits to establish the number of available tags,
and adjust the claim returns accordingly.

Cache the claimtag protocol availablity in the coresight_device to reduce
reads for the main claim/disclaim api.

changes since v1:
1) Added claim tag availability cache into coresight_device when using the
main coresight_claim_device() / coresight_disclaim_device() API.

Applies to coresight/next

Mike Leach (1):
  coresight: fix issue where coresight component has no claimtags

 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(-)

-- 
2.32.0