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authorJiri Kosina <jkosina@suse.cz>2013-05-28 10:09:22 +0200
committerJiri Kosina <jkosina@suse.cz>2013-05-28 10:09:29 +0200
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Merge branch 'master' into for-next
Merge with 49717cb ("kthread: Document ways of reducing OS jitter due to per-CPU kthreads") to be able to apply fixup patch on top of it. Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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@@ -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