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Documentation: amd-pstate: add amd pstate driver mode introduction 

The amd-pstate driver has two operation modes supported:
* CPPC Autonomous (active) mode
* CPPC non-autonomous (passive) mode.
active mode and passive mode can be chosen by different kernel parameters.

Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Wyes Karny <wyes.karny@amd.com>
Tested-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Perry Yuan 2023-01-31 17:00:13 +08:00 committed by Rafael J. Wysocki
parent abd61c08ef
commit 92e6088427
1 changed files with 24 additions and 2 deletions
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26
Documentation/admin-guide/pm/amd-pstate.rst
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@ -299,8 +299,30 @@ module which supports the new AMD P-States mechanism on most of the future AMD
platforms. The AMD P-States mechanism is the more performance and energy
efficiency frequency management method on AMD processors.
Kernel Module Options for ``amd-pstate``
=========================================
AMD Pstate Driver Operation Modes
=================================
``amd_pstate`` CPPC has two operation modes: CPPC Autonomous(active) mode and
CPPC non-autonomous(passive) mode.
active mode and passive mode can be chosen by different kernel parameters.
When in Autonomous mode, CPPC ignores requests done in the Desired Performance
Target register and takes into account only the values set to the Minimum requested
performance, Maximum requested performance, and Energy Performance Preference
registers. When Autonomous is disabled, it only considers the Desired Performance Target.
Active Mode
------------
``amd_pstate=active``
This is the low-level firmware control mode which is implemented by ``amd_pstate_epp``
driver with ``amd_pstate=active`` passed to the kernel in the command line.
In this mode, ``amd_pstate_epp`` driver provides a hint to the hardware if software
wants to bias toward performance (0x0) or energy efficiency (0xff) to the CPPC firmware.
then CPPC power algorithm will calculate the runtime workload and adjust the realtime
cores frequency according to the power supply and thermal, core voltage and some other
hardware conditions.
Passive Mode
------------