linux-kernel - [PATCH v7 13/13] Documentation: amd-pstate: introduce new global sysfs attributes

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Message-ID: <20221208111852.386731-14-perry.yuan@amd.com>
Date:   Thu, 8 Dec 2022 19:18:52 +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 v7 13/13] Documentation: amd-pstate: introduce new global sysfs attributes

The new amd-pstate driver support to switch the driver working mode and
use can switch the driver mode within the sysfs attributes in the below
path and check current mode

$ cd /sys/devices/system/cpu/amd-pstate

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

switch mode:
sudo bash -c "echo passive  > /sys/devices/system/cpu/amd-pstate/status"
or
sudo bash -c "echo active  > /sys/devices/system/cpu/amd-pstate/status"

Signed-off-by: Perry Yuan <perry.yuan@....com>
---
 Documentation/admin-guide/pm/amd-pstate.rst | 38 +++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
index 62744dae3c5f..b8e33db3957d 100644
--- a/Documentation/admin-guide/pm/amd-pstate.rst
+++ b/Documentation/admin-guide/pm/amd-pstate.rst
@@ -339,6 +339,44 @@ 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 "off".
+
+	"active"
+		The driver is functional and in the ``active mode``
+
+	"passive"
+		The driver is functional and in the ``passive mode``
+
+	"off"
+		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, the write will
+	cause the driver to switch over to the operation mode represented by
+	that string - or to be unregistered in the "off" case.
+
+``cppc_dynamic_boost``
+	This attribute is only present if ``amd-pstate`` works in the
+	`active mode` in the processor.  If set to 1, it will cause 
+        the minimum P-state limit to be increased dynamically for a short time
+        whenever a task previously waiting on I/O is selected to run on a given
+        logical CPU (the purpose of this mechanism is to improve performance).
+        when the I/O wait flag cleared, the increased pstate will be restored
+        to previous state.
+
+
 ``cpupower`` tool support for ``amd-pstate``
 ===============================================
 
-- 
2.34.1