Merge remote-tracking branch 'linux-pm/acpi-platform' into review-hans

Documentation/userspace-api/index.rst

@@ -24,6 +24,7 @@ place where this information is gathered.
    ioctl/index
    iommu
    media/index
+   sysfs-platform_profile
 
 .. only::  subproject and html
 

Documentation/userspace-api/sysfs-platform_profile.rst

@@ -0,0 +1,42 @@
+=====================================================================
+Platform Profile Selection (e.g. /sys/firmware/acpi/platform_profile)
+=====================================================================
+
+On modern systems the platform performance, temperature, fan and other
+hardware related characteristics are often dynamically configurable. The
+platform configuration is often automatically adjusted to the current
+conditions by some automatic mechanism (which may very well live outside
+the kernel).
+
+These auto platform adjustment mechanisms often can be configured with
+one of several platform profiles, with either a bias towards low power
+operation or towards performance.
+
+The purpose of the platform_profile attribute is to offer a generic sysfs
+API for selecting the platform profile of these automatic mechanisms.
+
+Note that this API is only for selecting the platform profile, it is
+NOT a goal of this API to allow monitoring the resulting performance
+characteristics. Monitoring performance is best done with device/vendor
+specific tools such as e.g. turbostat.
+
+Specifically when selecting a high performance profile the actual achieved
+performance may be limited by various factors such as: the heat generated
+by other components, room temperature, free air flow at the bottom of a
+laptop, etc. It is explicitly NOT a goal of this API to let userspace know
+about any sub-optimal conditions which are impeding reaching the requested
+performance level.
+
+Since numbers on their own cannot represent the multiple variables that a
+profile will adjust (power consumption, heat generation, etc) this API
+uses strings to describe the various profiles. To make sure that userspace
+gets a consistent experience the sysfs-platform_profile ABI document defines
+a fixed set of profile names. Drivers *must* map their internal profile
+representation onto this fixed set.
+
+If there is no good match when mapping then a new profile name may be
+added. Drivers which wish to introduce new profile names must:
+
+ 1. Explain why the existing profile names canot be used.
+ 2. Add the new profile name, along with a clear description of the
+    expected behaviour, to the sysfs-platform_profile ABI documentation.