[PATCH 4/4] Documentation: amd_pstate: Add amd_pstate state sysfs file

[Wyes Karny]

Add documentation for amd_pstate `state` interface.
User can see the current state of the driver with the help of this sysfs
interface:
  # cat /sys/devices/system/cpu/amd_pstate/state
  # disable [passive] guided

User can load/unload driver with the help of `state` sysfs interface.
- Load driver with passive mode:
  # echo passive > /sys/devices/system/cpu/amd_pstate/state
- Unload the driver:
  # echo disable > /sys/devices/system/cpu/amd_pstate/state
- To switch to guided mode:
  # echo guided > /sys/devices/system/cpu/amd_pstate/state

Signed-off-by: Wyes Karny <wyes.karny@xxxxxxx>
---
 Documentation/admin-guide/pm/amd-pstate.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
index 06e23538f79c..4d3783516ddc 100644
--- a/Documentation/admin-guide/pm/amd-pstate.rst
+++ b/Documentation/admin-guide/pm/amd-pstate.rst
@@ -265,6 +265,17 @@ This attribute is read-only.
 Other performance and frequency values can be read back from
 ``/sys/devices/system/cpu/cpuX/acpi_cppc/``, see :ref:`cppc_sysfs`.
 
+``state``
+
+``amd_pstate`` also exposes a sysfs interface to view and control the driver state.
+The driver state can be one of the following:
+``disable``     : indicates driver is in unloaded state.
+``passive``     : indicates driver is loaded and currently in passive mode.
+``guided`` : indicates driver is loaded and currenlty in guided autonomous mode.
+This file can be found here: ``/sys/devices/system/cpu/amd_pstate/state``.
+
+To switch to passive mode: ``echo passive > /sys/devices/system/cpu/amd_pstate/state``
+To switch to guided mode: ``echo guided > /sys/devices/system/cpu/amd_pstate/state``
 
 ``amd-pstate`` vs ``acpi-cpufreq``
 ======================================
-- 
2.34.1