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

	- Power management user interface in /sys/power

	- Power management user interface in /sys/power

notifiers.txt

notifiers.txt

	- Registering suspend notifiers in device drivers

	- Registering suspend notifiers in device drivers

opp.txt

	- Operating Performance Point library

pci.txt

pci.txt

	- How the PCI Subsystem Does Power Management

	- How the PCI Subsystem Does Power Management

pm_qos_interface.txt

pm_qos_interface.txt

*=============*

* 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))

			soc_switch_to_freq_voltage(freq);

		else

			/* do something when we cant satisfy the req */

		/* do other stuff */

	 }

4. OPP Availability Control Functions

=====================================

A default OPP list registered with the OPP library may not cater to all possible

situation. The OPP library provides a set of functions to modify the

availability of a OPP within the OPP list. This allows SoC frameworks to have

fine grained dynamic control of which sets of OPPs are operationally available.

These functions are intended to *temporarily* remove an OPP in conditions such

as thermal considerations (e.g. don't use OPPx until the temperature drops).

WARNING: Do not use these functions in interrupt context.

opp_enable - Make a OPP available for operation.

	Example: Lets say that 1GHz OPP is to be made available only if the

	SoC temperature is lower than a certain threshold. The SoC framework

	implementation might choose to do something as follows:

	 if (cur_temp < temp_low_thresh) {

		/* Enable 1GHz if it was disabled */

		rcu_read_lock();

		opp = opp_find_freq_exact(dev, 1000000000, false);

		rcu_read_unlock();

		/* just error check */

		if (!IS_ERR(opp))

			ret = opp_enable(dev, 1000000000);

		else

			goto try_something_else;

	 }

opp_disable - Make an OPP to be not available for operation

	Example: Lets say that 1GHz OPP is to be disabled if the temperature

	exceeds a threshold value. The SoC framework implementation might

	choose to do something as follows:

	 if (cur_temp > temp_high_thresh) {

		/* Disable 1GHz if it was enabled */

		rcu_read_lock();

		opp = opp_find_freq_exact(dev, 1000000000, true);

		rcu_read_unlock();

		/* just error check */

		if (!IS_ERR(opp))

			ret = opp_disable(dev, 1000000000);

		else

			goto try_something_else;

	 }

5. OPP Data Retrieval Functions

===============================

Since OPP library abstracts away the OPP information, a set of functions to pull

information from the OPP structure is necessary. Once an OPP pointer is

retrieved using the search functions, the following functions can be used by SoC

framework to retrieve the information represented inside the OPP layer.

opp_get_voltage - Retrieve the voltage represented by the opp pointer.

	Example: At a cpufreq transition to a different frequency, SoC

	framework requires to set the voltage represented by the OPP using

	the regulator framework to the Power Management chip providing the

	voltage.

	 soc_switch_to_freq_voltage(freq)

	 {

		/* do things */

		rcu_read_lock();

		opp = opp_find_freq_ceil(dev, &freq);

		v = opp_get_voltage(opp);

		rcu_read_unlock();

		if (v)

			regulator_set_voltage(.., v);

		/* do other things */

	 }

opp_get_freq - Retrieve the freq represented by the opp pointer.

	Example: Lets say the SoC framework uses a couple of helper functions

	we could pass opp pointers instead of doing additional parameters to

	handle quiet a bit of data parameters.

	 soc_cpufreq_target(..)

	 {

		/* do things.. */

		 max_freq = ULONG_MAX;

		 rcu_read_lock();

		 max_opp = opp_find_freq_floor(dev,&max_freq);

		 requested_opp = opp_find_freq_ceil(dev,&freq);

		 if (!IS_ERR(max_opp) && !IS_ERR(requested_opp))

			r = soc_test_validity(max_opp, requested_opp);

		 rcu_read_unlock();

		/* do other things */

	 }

	 soc_test_validity(..)

	 {

		 if(opp_get_voltage(max_opp) < opp_get_voltage(requested_opp))

			 return -EINVAL;

		 if(opp_get_freq(max_opp) < opp_get_freq(requested_opp))

			 return -EINVAL;

		/* do things.. */

	 }

opp_get_opp_count - Retrieve the number of available opps for a device

	Example: Lets say a co-processor in the SoC needs to know the available

	frequencies in a table, the main processor can notify as following:

	 soc_notify_coproc_available_frequencies()

	 {

		/* Do things */

		rcu_read_lock();

		num_available = opp_get_opp_count(dev);

		speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL);

		/* populate the table in increasing order */

		freq = 0;

		while (!IS_ERR(opp = opp_find_freq_ceil(dev, &freq))) {

			speeds[i] = freq;

			freq++;

			i++;

		}

		rcu_read_unlock();

		soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available);

		/* Do other things */

	 }

6. Cpufreq Table Generation

===========================

opp_init_cpufreq_table - cpufreq framework typically is initialized with

	cpufreq_frequency_table_cpuinfo which is provided with the list of

	frequencies that are available for operation. This function provides

	a ready to use conversion routine to translate the OPP layer's internal

	information about the available frequencies into a format readily

	providable to cpufreq.

	WARNING: Do not use this function in interrupt context.

	Example:

	 soc_pm_init()

	 {

		/* Do things */

		r = opp_init_cpufreq_table(dev, &freq_table);

		if (!r)

			cpufreq_frequency_table_cpuinfo(policy, freq_table);

		/* Do other things */

	 }

	NOTE: This function is available only if CONFIG_CPU_FREQ is enabled in

	addition to CONFIG_PM as power management feature is required to

	dynamically scale voltage and frequency in a system.

7. Data Structures

==================

Typically an SoC contains multiple voltage domains which are variable. Each

domain is represented by a device pointer. The relationship to OPP can be

represented as follows:

SoC

 |- device 1

 |	|- opp 1 (availability, freq, voltage)

 |	|- opp 2 ..

 ...	...

 |	`- opp n ..

 |- device 2

 ...

 `- device m

OPP library maintains a internal list that the SoC framework populates and

accessed by various functions as described above. However, the structures

representing the actual OPPs and domains are internal to the OPP library itself

to allow for suitable abstraction reusable across systems.

struct opp - The internal data structure of OPP library which is used to

	represent an OPP. In addition to the freq, voltage, availability

	information, it also contains internal book keeping information required

	for the OPP library to operate on.  Pointer to this structure is

	provided back to the users such as SoC framework to be used as a

	identifier for OPP in the interactions with OPP layer.

	WARNING: The struct opp pointer should not be parsed or modified by the

	users. The defaults of for an instance is populated by opp_add, but the

	availability of the OPP can be modified by opp_enable/disable functions.

struct device - This is used to identify a domain to the OPP layer. The

	nature of the device and it's implementation is left to the user of

	OPP library such as the SoC framework.

Overall, in a simplistic view, the data structure operations is represented as

following:

Initialization / modification:

            +-----+        /- opp_enable

opp_add --> | opp | <-------

  |         +-----+        \- opp_disable

  \-------> domain_info(device)

Search functions:

             /-- opp_find_freq_ceil  ---\   +-----+

domain_info<---- opp_find_freq_exact -----> | opp |

             \-- opp_find_freq_floor ---/   +-----+

Retrieval functions:

+-----+     /- opp_get_voltage

| opp | <---

+-----+     \- opp_get_freq

domain_info <- opp_get_opp_count

obj-$(CONFIG_PM_RUNTIME)	+= runtime.o

obj-$(CONFIG_PM_RUNTIME)	+= runtime.o

obj-$(CONFIG_PM_OPS)	+= generic_ops.o

obj-$(CONFIG_PM_OPS)	+= generic_ops.o

obj-$(CONFIG_PM_TRACE_RTC)	+= trace.o

obj-$(CONFIG_PM_TRACE_RTC)	+= trace.o

obj-$(CONFIG_PM_OPP)	+= opp.o

ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG

ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG

ccflags-$(CONFIG_PM_VERBOSE)   += -DDEBUG

ccflags-$(CONFIG_PM_VERBOSE)   += -DDEBUG

/*

 * Generic OPP Interface

 *

 * Copyright (C) 2009-2010 Texas Instruments Incorporated.

 *	Nishanth Menon

 *	Romit Dasgupta

 *	Kevin Hilman

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 */

#ifndef __LINUX_OPP_H__

#define __LINUX_OPP_H__

#include <linux/err.h>

#include <linux/cpufreq.h>

struct opp;

#if defined(CONFIG_PM_OPP)

unsigned long opp_get_voltage(struct opp *opp);

unsigned long opp_get_freq(struct opp *opp);

int opp_get_opp_count(struct device *dev);

struct opp *opp_find_freq_exact(struct device *dev, unsigned long freq,

				bool available);

struct opp *opp_find_freq_floor(struct device *dev, unsigned long *freq);

struct opp *opp_find_freq_ceil(struct device *dev, unsigned long *freq);

int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt);

int opp_enable(struct device *dev, unsigned long freq);

int opp_disable(struct device *dev, unsigned long freq);

#else

static inline unsigned long opp_get_voltage(struct opp *opp)

{

	return 0;

}

static inline unsigned long opp_get_freq(struct opp *opp)

{

	return 0;

}

static inline int opp_get_opp_count(struct device *dev)

{

	return 0;

}

static inline struct opp *opp_find_freq_exact(struct device *dev,

					unsigned long freq, bool available)

{

	return ERR_PTR(-EINVAL);

}

static inline struct opp *opp_find_freq_floor(struct device *dev,

					unsigned long *freq)

{

	return ERR_PTR(-EINVAL);

}

static inline struct opp *opp_find_freq_ceil(struct device *dev,

					unsigned long *freq)

{

	return ERR_PTR(-EINVAL);

}

static inline int opp_add(struct device *dev, unsigned long freq,

					unsigned long u_volt)

{

	return -EINVAL;

}

static inline int opp_enable(struct device *dev, unsigned long freq)

{

	return 0;

}

static inline int opp_disable(struct device *dev, unsigned long freq)

{

	return 0;

}

#endif		/* CONFIG_PM */

#if defined(CONFIG_CPU_FREQ) && defined(CONFIG_PM_OPP)

int opp_init_cpufreq_table(struct device *dev,

			    struct cpufreq_frequency_table **table);

#else

static inline int opp_init_cpufreq_table(struct device *dev,

			    struct cpufreq_frequency_table **table)

{

	return -EINVAL;

}

#endif		/* CONFIG_CPU_FREQ */

#endif		/* __LINUX_OPP_H__ */