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coresight: etm4x: Do not access TRCIDR1 for identification

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commit 735e7b30a5 upstream.

CoreSight ETM4x architecture clearly provides ways to identify a device
via registers in the "Management" class, TRCDEVARCH and TRCDEVTYPE. These
registers can be accessed without the Trace domain being powered on.
We additionally added TRCIDR1 as fallback in order to cover for any
ETMs that may not have implemented TRCDEVARCH. So far, nobody has
reported hitting a WARNING we placed to catch such systems.

Also, more importantly it is problematic to access TRCIDR1, which is a
"Trace" register via MMIO access, without clearing the OSLK. But we cannot
mess with the OSLK until we know for sure that this is an ETMv4 device.
Thus, this kind of creates a chicken and egg problem unnecessarily for
systems "which are compliant" to the ETMv4 architecture.

Let us remove the TRCIDR1 fall back check and rely only on TRCDEVARCH.

Fixes: 8b94db1eda ("coresight: etm4x: Use TRCDEVARCH for component discovery")
Cc: stable@vger.kernel.org
Reported-by: Steve Clevenger <scclevenger@os.amperecomputing.com>
Link: https://lore.kernel.org/all/143540e5623d4c7393d24833f2b80600d8d745d2.1677881753.git.scclevenger@os.amperecomputing.com/
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230321104530.1547136-1-suzuki.poulose@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Suzuki K Poulose 2023-03-21 10:45:30 +00:00 • committed by Greg Kroah-Hartman
commit 13ec3c238f
2 changed files with 15 additions and 27 deletions
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