linux-kernel - [PATCH v10 12/12] Documentation: amd-pstate: introduce new global sysfs attributes

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Date:   Fri, 6 Jan 2023 14:14:20 +0800
From:   Perry Yuan <perry.yuan@....com>
To:     <rafael.j.wysocki@...el.com>, <Mario.Limonciello@....com>,
        <ray.huang@....com>, <viresh.kumar@...aro.org>
CC:     <Deepak.Sharma@....com>, <Nathan.Fontenot@....com>,
        <Alexander.Deucher@....com>, <Shimmer.Huang@....com>,
        <Xiaojian.Du@....com>, <Li.Meng@....com>, <wyes.karny@....com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v10 12/12] Documentation: amd-pstate: introduce new global sysfs attributes

The amd-pstate driver supports switching working modes at runtime.
Users can view and change modes by interacting with the "status" sysfs
attribute.

1) check driver mode:
$ cat /sys/devices/system/cpu/amd-pstate/status

2) switch mode:
`# echo "passive" | sudo tee /sys/devices/system/cpu/amd-pstate/status`
or
`# echo "active" | sudo tee /sys/devices/system/cpu/amd-pstate/status`

Reviewed-by: Mario Limonciello <mario.limonciello@....com>
Signed-off-by: Perry Yuan <perry.yuan@....com>
---
 Documentation/admin-guide/pm/amd-pstate.rst | 29 +++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
index 62744dae3c5f..df0637a49f47 100644
--- a/Documentation/admin-guide/pm/amd-pstate.rst
+++ b/Documentation/admin-guide/pm/amd-pstate.rst
@@ -339,6 +339,35 @@ processor must provide at least nominal performance requested and go higher if c
 operating conditions allow.
 
 
+User Space Interface in ``sysfs``
+=================================
+
+Global Attributes
+-----------------
+
+``amd-pstate`` exposes several global attributes (files) in ``sysfs`` to
+control its functionality at the system level.  They are located in the
+``/sys/devices/system/cpu/amd-pstate/`` directory and affect all CPUs.
+
+``status``
+	Operation mode of the driver: "active", "passive" or "disable".
+
+	"active"
+		The driver is functional and in the ``active mode``
+
+	"passive"
+		The driver is functional and in the ``passive mode``
+
+	"disable"
+		The driver is unregistered and not functional now.
+
+        This attribute can be written to in order to change the driver's
+        operation mode or to unregister it.  The string written to it must be
+        one of the possible values of it and, if successful, writing one of
+        these values to the sysfs file will cause the driver to switch over
+        to the operation mode represented by that string - or to be
+        unregistered in the "disable" case.
+
 ``cpupower`` tool support for ``amd-pstate``
 ===============================================
 
-- 
2.34.1