From fb1fe1041c04ee5ba362cf239e83a7c559beb0f3 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Date: Thu, 5 Jan 2017 02:53:12 +0100
Subject: cpufreq: intel_pstate: Operation mode control from sysfs

Make it possible to change the operation mode of intel_pstate with
the help of a new sysfs attribute called "status".

There are three possible configurations that can be selected using
this attribute:

 "off"     - The driver is not in use at this time.
 "active"  - The driver works as a P-state governor (default).
 "passive" - The driver works as a regular cpufreq one and collaborates
             with the generic cpufreq governors (it sets P-states as
             requested by those governors).  [This is the same mode
             the driver can be started in by passing intel_pstate=passive
             in the kernel command line.]

The current setting is returned by reads from this attribute.  Writing
one of the above strings to it changes the operation mode as indicated
by that string, if possible.

If HW-managed P-states (HWP) feature is enabled, it is not possible
to change the driver's operation mode and attempts to write to this
attribute will fail.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 Documentation/cpu-freq/intel-pstate.txt | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'Documentation/cpu-freq')

diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
index 1953994ef5e6..3fdcdfd968ba 100644
--- a/Documentation/cpu-freq/intel-pstate.txt
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -85,6 +85,21 @@ Sysfs will show :
 Refer to "Intel® 64 and IA-32 Architectures Software Developer’s Manual
 Volume 3: System Programming Guide" to understand ratios.
 
+There is one more sysfs attribute in /sys/devices/system/cpu/intel_pstate/
+that can be used for controlling the operation mode of the driver:
+
+      status: Three settings are possible:
+      "off"     - The driver is not in use at this time.
+      "active"  - The driver works as a P-state governor (default).
+      "passive" - The driver works as a regular cpufreq one and collaborates
+                  with the generic cpufreq governors (it sets P-states as
+                  requested by those governors).
+      The current setting is returned by reads from this attribute.  Writing one
+      of the above strings to it changes the operation mode as indicated by that
+      string, if possible.  If HW-managed P-states (HWP) are enabled, it is not
+      possible to change the driver's operation mode and attempts to write to
+      this attribute will fail.
+
 cpufreq sysfs for Intel P-State
 
 Since this driver registers with cpufreq, cpufreq sysfs is also presented.
-- 
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