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On Intel processors, the core frequency can be reduced below OS request, when the current temperature reaches the TCC (Thermal Control Circuit) activation temperature. The default TCC activation temperature is specified by MSR_IA32_TEMPERATURE_TARGET. However, it can be adjusted by specifying an offset in degrees C, using the TCC Offset bits in the same MSR register. This patch introduces a cooling devices driver that utilizes the TCC Offset feature. The bigger the current cooling state is, the lower the effective TCC activation temperature is, so that the processors can be throttled earlier before system critical overheats. Note that, on different platforms, the behavior might be different on how fast the setting takes effect, and how much the CPU frequency is reduced. This patch has been tested on a KabyLake mobile platform from me, and also on a CometLake platform from Doug. Signed-off-by: Zhang Rui <rui.zhang@intel.com> Tested by: Doug Smythies <dsmythies@telus.net> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> Link: https://lore.kernel.org/r/20210412125901.12549-1-rui.zhang@intel.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 Restructured Text 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.