[PATCH v3] coresight: ete: Always save state on power down

[Leo Yan]

On Tue, May 05, 2026 at 05:51:25PM +0100, James Clark wrote:
> System register ETMs and ETE are unlikely to be preserved on CPU power
> down. The ETE DT binding also never documented
> "arm,coresight-loses-context-with-cpu" so nobody would have legitimately
> been able to use that binding to fix it and ACPI has no such binding at
> all.
> 
> Fix it by hard coding the setting for sysreg ETMs (ETE is always sysreg)
> or ACPI boots. Use a local variable when setting up save_state so that
> it's immune to concurrent probing when devices have different
> configurations which is an issue with modifying the global.
> 
> This fixes the following error when using Coresight with ACPI on the FVP
> which supports CPU PM:
> 
>   coresight ete0: External agent took claim tag
>   WARNING: drivers/hwtracing/coresight/coresight-core.c:248 at coresight_disclaim_device_unlocked+0xe0/0xe8, CPU#0: perf/117
> 
> Fixes: 35e1c9163e02 ("coresight: ete: Add support for ETE tracing")
> Signed-off-by: James Clark <james.clark at linaro.org>

Reviewed-by: Leo Yan <leo.yan at arm.com>