Documentation/admin-guide/pm/cpufreq_drivers.rst

Source file repositories/reference/linux-study-clean/Documentation/admin-guide/pm/cpufreq_drivers.rst

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Documentation/admin-guide/pm/cpufreq_drivers.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0

=======================================================
Legacy Documentation of CPU Performance Scaling Drivers
=======================================================

Included below are historic documents describing assorted
:doc:`CPU performance scaling <cpufreq>` drivers.  They are reproduced verbatim,
with the original white space formatting and indentation preserved, except for
the added leading space character in every line of text.


AMD PowerNow! Drivers
=====================

::

 PowerNow! and Cool'n'Quiet are AMD names for frequency
 management capabilities in AMD processors. As the hardware
 implementation changes in new generations of the processors,
 there is a different cpu-freq driver for each generation.

 Note that the driver's will not load on the "wrong" hardware,
 so it is safe to try each driver in turn when in doubt as to
 which is the correct driver.

 Note that the functionality to change frequency (and voltage)
 is not available in all processors. The drivers will refuse
 to load on processors without this capability. The capability
 is detected with the cpuid instruction.

 The drivers use BIOS supplied tables to obtain frequency and
 voltage information appropriate for a particular platform.
 Frequency transitions will be unavailable if the BIOS does
 not supply these tables.

 6th Generation: powernow-k6

 7th Generation: powernow-k7: Athlon, Duron, Geode.

 8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
 Documentation on this functionality in 8th generation processors
 is available in the "BIOS and Kernel Developer's Guide", publication
 26094, in chapter 9, available for download from www.amd.com.

 BIOS supplied data, for powernow-k7 and for powernow-k8, may be
 from either the PSB table or from ACPI objects. The ACPI support
 is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
 The powernow-k8 driver will attempt to use ACPI if so configured,
 and fall back to PST if that fails.
 The powernow-k7 driver will try to use the PSB support first, and
 fall back to ACPI if the PSB support fails. A module parameter,
 acpi_force, is provided to force ACPI support to be used instead
 of PSB support.


``cpufreq-nforce2``
===================

::

 The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.

 This works better than on other platforms, because the FSB of the CPU
 can be controlled independently from the PCI/AGP clock.

 The module has two options:

 	fid: 	 multiplier * 10 (for example 8.5 = 85)
 	min_fsb: minimum FSB

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Implementation Notes