PM: Introduce library for device-specific OPPs (v7)

SoCs have a standard set of tuples consisting of frequency and
voltage pairs that the device will support per voltage domain. These
are called Operating Performance Points or OPPs. The actual
definitions of OPP varies over silicon versions. For a specific domain,
we can have a set of {frequency, voltage} pairs. As the kernel boots
and more information is available, a default set of these are activated
based on the precise nature of device. Further on operation, based on
conditions prevailing in the system (such as temperature), some OPP
availability may be temporarily controlled by the SoC frameworks.

To implement an OPP, some sort of power management support is necessary
hence this library depends on CONFIG_PM.

Contributions include:
Sanjeev Premi for the initial concept:
	http://patchwork.kernel.org/patch/50998/
Kevin Hilman for converting original design to device-based.
Kevin Hilman and Paul Walmsey for cleaning up many of the function
abstractions, improvements and data structure handling.
Romit Dasgupta for using enums instead of opp pointers.
Thara Gopinath, Eduardo Valentin and Vishwanath BS for fixes and
cleanups.
Linus Walleij for recommending this layer be made generic for usage
in other architectures beyond OMAP and ARM.
Mark Brown, Andrew Morton, Rafael J. Wysocki, Paul E. McKenney for
valuable improvements.

Discussions and comments from:
http://marc.info/?l=linux-omap&m=126033945313269&w=2
http://marc.info/?l=linux-omap&m=125482970102327&w=2
http://marc.info/?t=125809247500002&r=1&w=2
http://marc.info/?l=linux-omap&m=126025973426007&w=2
http://marc.info/?t=128152609200064&r=1&w=2
http://marc.info/?t=128468723000002&r=1&w=2
incorporated.

v1: http://marc.info/?t=128468723000002&r=1&w=2

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

6 files changed, 1125 insertions, 0 deletions

diff --git a/Documentation/power/00-INDEX b/Documentation/power/00-INDEX
index fb742c213c9e..45e9d4a91284 100644
--- a/Documentation/power/00-INDEX
+++ b/Documentation/power/00-INDEX
@@ -14,6 +14,8 @@ interface.txt
         - Power management user interface in /sys/power
 notifiers.txt
         - Registering suspend notifiers in device drivers
+opp.txt
+        - Operating Performance Point library
 pci.txt
         - How the PCI Subsystem Does Power Management
 pm_qos_interface.txt
diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt
new file mode 100644
index 000000000000..44d87ad3cea9
--- /dev/null
+++ b/Documentation/power/opp.txt
@@ -0,0 +1,375 @@
+*=============*
+* OPP Library *
+*=============*
+
+(C) 2009-2010 Nishanth Menon <nm@ti.com>, Texas Instruments Incorporated
+
+Contents
+--------
+1. Introduction
+2. Initial OPP List Registration
+3. OPP Search Functions
+4. OPP Availability Control Functions
+5. OPP Data Retrieval Functions
+6. Cpufreq Table Generation
+7. Data Structures
+
+1. Introduction
+===============
+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
+the device will support per domain are called Operating Performance Points or
+OPPs.
+
+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
+CONFIG_PM_OPP from power management menuconfig menu. OPP library depends on
+CONFIG_PM as certain SoCs such as Texas Instrument's OMAP framework allows to
+optionally boot at a certain OPP without needing cpufreq.
+
+Typical usage of the OPP library is as follows:
+(users)         -> registers a set of default OPPs              -> (library)
+SoC framework   -> modifies on required cases certain OPPs      -> OPP layer
+                -> queries to search/retrieve information       ->
+
+OPP layer expects each domain to be represented by a unique device pointer. SoC
+framework registers a set of initial OPPs per device with the OPP layer. This
+list is expected to be an optimally small number typically around 5 per device.
+This initial list contains a set of OPPs that the framework expects to be safely
+enabled by default in the system.
+
+Note on OPP Availability:
+------------------------
+As the system proceeds to operate, SoC framework may choose to make certain
+OPPs available or not available on each device based on various external
+factors. Example usage: Thermal management or other exceptional situations where
+SoC framework might choose to disable a higher frequency OPP to safely continue
+operations until that OPP could be re-enabled if possible.
+
+OPP library facilitates this concept in it's implementation. The following
+operational functions operate only on available opps:
+opp_find_freq_{ceil, floor}, opp_get_voltage, opp_get_freq, opp_get_opp_count
+and opp_init_cpufreq_table
+
+opp_find_freq_exact is meant to be used to find the opp pointer which can then
+be used for opp_enable/disable functions to make an opp available as required.
+
+WARNING: Users of OPP library should refresh their availability count using
+get_opp_count if opp_enable/disable functions are invoked for a device, the
+exact mechanism to trigger these or the notification mechanism to other
+dependent subsystems such as cpufreq are left to the discretion of the SoC
+specific framework which uses the OPP library. Similar care needs to be taken
+care to refresh the cpufreq table in cases of these operations.
+
+WARNING on OPP List locking mechanism:
+-------------------------------------------------
+OPP library uses RCU for exclusivity. RCU allows the query functions to operate
+in multiple contexts and this synchronization mechanism is optimal for a read
+intensive operations on data structure as the OPP library caters to.
+
+To ensure that the data retrieved are sane, the users such as SoC framework
+should ensure that the section of code operating on OPP queries are locked
+using RCU read locks. The opp_find_freq_{exact,ceil,floor},
+opp_get_{voltage, freq, opp_count} fall into this category.
+
+opp_{add,enable,disable} are updaters which use mutex and implement it's own
+RCU locking mechanisms. opp_init_cpufreq_table acts as an updater and uses
+mutex to implment RCU updater strategy. These functions should *NOT* be called
+under RCU locks and other contexts that prevent blocking functions in RCU or
+mutex operations from working.
+
+2. Initial OPP List Registration
+================================
+The SoC implementation calls opp_add function iteratively to add OPPs per
+device. It is expected that the SoC framework will register the OPP entries
+optimally- typical numbers range to be less than 5. The list generated by
+registering the OPPs is maintained by OPP library throughout the device
+operation. The SoC framework can subsequently control the availability of the
+OPPs dynamically using the opp_enable / disable functions.
+
+opp_add - Add a new OPP for a specific domain represented by the device pointer.
+        The OPP is defined using the frequency and voltage. Once added, the OPP
+        is assumed to be available and control of it's availability can be done
+        with the opp_enable/disable functions. OPP library internally stores
+        and manages this information in the opp struct. This function may be
+        used by SoC framework to define a optimal list as per the demands of
+        SoC usage environment.
+
+        WARNING: Do not use this function in interrupt context.
+
+        Example:
+         soc_pm_init()
+         {
+                /* Do things */
+                r = opp_add(mpu_dev, 1000000, 900000);
+                if (!r) {
+                        pr_err("%s: unable to register mpu opp(%d)\n", r);
+                        goto no_cpufreq;
+                }
+                /* Do cpufreq things */
+         no_cpufreq:
+                /* Do remaining things */
+         }
+
+3. OPP Search Functions
+=======================
+High level framework such as cpufreq operates on frequencies. To map the
+frequency back to the corresponding OPP, OPP library provides handy functions
+to search the OPP list that OPP library internally manages. These search
+functions return the matching pointer representing the opp if a match is
+found, else returns error. These errors are expected to be handled by standard
+error checks such as IS_ERR() and appropriate actions taken by the caller.
+
+opp_find_freq_exact - Search for an OPP based on an *exact* frequency and
+        availability. This function is especially useful to enable an OPP which
+        is not available by default.
+        Example: In a case when SoC framework detects a situation where a
+        higher frequency could be made available, it can use this function to
+        find the OPP prior to call the opp_enable to actually make it available.
+         rcu_read_lock();
+         opp = opp_find_freq_exact(dev, 1000000000, false);
+         rcu_read_unlock();
+         /* dont operate on the pointer.. just do a sanity check.. */
+         if (IS_ERR(opp)) {
+                pr_err("frequency not disabled!\n");
+                /* trigger appropriate actions.. */
+         } else {
+                opp_enable(dev,1000000000);
+         }
+
+        NOTE: This is the only search function that operates on OPPs which are
+        not available.
+
+opp_find_freq_floor - Search for an available OPP which is *at most* the
+        provided frequency. This function is useful while searching for a lesser
+        match OR operating on OPP information in the order of decreasing
+        frequency.
+        Example: To find the highest opp for a device:
+         freq = ULONG_MAX;
+         rcu_read_lock();
+         opp_find_freq_floor(dev, &freq);
+         rcu_read_unlock();
+
+opp_find_freq_ceil - Search for an available OPP which is *at least* the
+        provided frequency. This function is useful while searching for a
+        higher match OR operating on OPP information in the order of increasing
+        frequency.
+        Example 1: To find the lowest opp for a device:
+         freq = 0;
+         rcu_read_lock();
+         opp_find_freq_ceil(dev, &freq);
+         rcu_read_unlock();
+        Example 2: A simplified implementation of a SoC cpufreq_driver->target:
+         soc_cpufreq_target(..)
+         {
+                /* Do stuff like policy checks etc. */
+                /* Find the best frequency match for the req */
+                rcu_read_lock();
+                opp = opp_find_freq_ceil(dev, &freq);
+                rcu_read_unlock();
+                if (!IS_ERR(opp))