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authorNishanth Menon <nm@ti.com>2013-02-26 23:53:02 +0000
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-03-04 14:23:11 +0100
commit4b87581036849723242cadaa161e9b01234ef9ae (patch)
tree4a118f2419870b9bb177b714c2075cfb22eb17ae /Documentation/power
parente5dde92cb2befb108ae8cfe8db68a954c164d77c (diff)
downloadlinux-4b87581036849723242cadaa161e9b01234ef9ae.tar.gz
PM / OPP: improve introductory documentation
Make Operating Performance Points (OPP) library introductory chapter a little more reader-friendly. Split the chapter into two sections, highlight the definition with an example and minor rewording to be verbose. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Nishanth Menon <nm@ti.com> Reviewed-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'Documentation/power')
-rw-r--r--Documentation/power/opp.txt25
1 files changed, 20 insertions, 5 deletions
diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt
index 3035d00757a..425c51d56ae 100644
--- a/Documentation/power/opp.txt
+++ b/Documentation/power/opp.txt
@@ -1,6 +1,5 @@
-*=============*
-* OPP Library *
-*=============*
+Operating Performance Points (OPP) Library
+==========================================
(C) 2009-2010 Nishanth Menon <nm@ti.com>, Texas Instruments Incorporated
@@ -16,15 +15,31 @@ Contents
1. Introduction
===============
+1.1 What is an Operating Performance Point (OPP)?
+
Complex SoCs of today consists of a multiple sub-modules working in conjunction.
In an operational system executing varied use cases, not all modules in the SoC
need to function at their highest performing frequency all the time. To
facilitate this, sub-modules in a SoC are grouped into domains, allowing some
-domains to run at lower voltage and frequency while other domains are loaded
-more. The set of discrete tuples consisting of frequency and voltage pairs that
+domains to run at lower voltage and frequency while other domains run at
+voltage/frequency pairs that are higher.
+
+The set of discrete tuples consisting of frequency and voltage pairs that
the device will support per domain are called Operating Performance Points or
OPPs.
+As an example:
+Let us consider an MPU device which supports the following:
+{300MHz at minimum voltage of 1V}, {800MHz at minimum voltage of 1.2V},
+{1GHz at minimum voltage of 1.3V}
+
+We can represent these as three OPPs as the following {Hz, uV} tuples:
+{300000000, 1000000}
+{800000000, 1200000}
+{1000000000, 1300000}
+
+1.2 Operating Performance Points Library
+
OPP library provides a set of helper functions to organize and query the OPP
information. The library is located in drivers/base/power/opp.c and the header
is located in include/linux/opp.h. OPP library can be enabled by enabling