[PATCH v8 1/3] Documentation: Add documentation for new platform_profile sysfs attribute

[Mark Pearson <markpearson@lenovo.com>]

On modern systems the platform performance, temperature, fan and other
hardware related characteristics are often dynamically configurable. The
profile is often automatically adjusted to the load 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
consumption or towards performance (and higher power consumption and
thermals).

Introduce a new platform_profile sysfs API which offers a generic API for
selecting the performance-profile of these automatic-mechanisms.

Co-developed-by: Mark Pearson <markpearson@lenovo.com>
Signed-off-by: Mark Pearson <markpearson@lenovo.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v2:
 - updated to rst format
Changes in v3, v4, v5
 - version bump along with rest of patch series
Changes in v6:
 - Split sysfs-platform_profile.rs into ABI text and then admin guide in
   userspace-api section. Hope this is correct - I'm guessing a bit.
Changes in v7:
 - Correct available_choices to platform_profile_choices
 - Improve phrasing as recommended by review
Changes in v8:
 - Removed unnecessary empty lines at end of file

 .../ABI/testing/sysfs-platform_profile        | 24 +++++++++++
 Documentation/userspace-api/index.rst         |  1 +
 .../userspace-api/sysfs-platform_profile.rst  | 42 +++++++++++++++++++
 3 files changed, 67 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-platform_profile
 create mode 100644 Documentation/userspace-api/sysfs-platform_profile.rst

diff --git a/Documentation/ABI/testing/sysfs-platform_profile b/Documentation/ABI/testing/sysfs-platform_profile
new file mode 100644
index 000000000000..9d6b89b66cca
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-platform_profile
@@ -0,0 +1,24 @@
+What:		/sys/firmware/acpi/platform_profile_choices
+Date:		October 2020
+Contact:	Hans de Goede <hdegoede@redhat.com>
+Description:	This file contains a space-separated list of profiles supported for this device.
+
+		Drivers must use the following standard profile-names:
+
+		============	============================================
+		low-power	Low power consumption
+		cool		Cooler operation
+		quiet		Quieter operation
+		balanced	Balance between low power consumption and performance
+		performance	High performance operation
+		============	============================================
+
+		Userspace may expect drivers to offer more than one of these
+		standard profile names.
+
+What:		/sys/firmware/acpi/platform_profile
+Date:		October 2020
+Contact:	Hans de Goede <hdegoede@redhat.com>
+Description:	Reading this file gives the current selected profile for this
+		device. Writing this file with one of the strings from
+		platform_profile_choices changes the profile to the new value.
diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index acd2cc2a538d..d29b020e5622 100644
--- a/Documentation/userspace-api/index.rst
+++ b/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
 
diff --git a/Documentation/userspace-api/sysfs-platform_profile.rst b/Documentation/userspace-api/sysfs-platform_profile.rst
new file mode 100644
index 000000000000..c33a71263d9e
--- /dev/null
+++ b/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.
-- 
2.28.0