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If a CPU supports FEAT_TRF, as described in the section K5.5 "Context
switching", Arm ARM (ARM DDI 0487 L.a), it defines a flow to prohibit
program-flow trace, execute a TSB CSYNC instruction for flushing,
followed by clearing TRCPRGCTLR.EN bit.
To restore the state, the reverse sequence is required.
This differs from the procedure described in the section 3.4.1 "The
procedure when powering down the PE" of ARM IHI0064H.b, which involves
the OS Lock to prevent external debugger accesses and implicitly
disables trace.
To be compatible with different ETM versions, explicitly control trace
unit using etm4_disable_trace_unit() and etm4_enable_trace_unit()
during CPU idle to comply with FEAT_TRF.
As a result, the save states for TRFCR_ELx and trcprgctlr are redundant,
remove them.
Fixes: f188b5e76aae ("coresight: etm4x: Save/restore state across CPU low power states")
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251111-arm_coresight_power_management_fix-v6-6-f55553b6c8b3@arm.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.