[mirror_ubuntu-bionic-kernel.git] / Documentation / power / opp.txt

Operating Performance Points (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. Data Structures

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 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/pm_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}, dev_pm_opp_get_voltage, dev_pm_opp_get_freq, dev_pm_opp_get_opp_count

dev_pm_opp_find_freq_exact is meant to be used to find the opp pointer which can then
be used for dev_pm_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 dev_pm_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.

2. Initial OPP List Registration
================================
The SoC implementation calls dev_pm_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 dev_pm_opp_enable / disable functions.

dev_pm_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 dev_pm_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 = dev_pm_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.

Callers of these functions shall call dev_pm_opp_put() after they have used the
OPP. Otherwise the memory for the OPP will never get freed and result in
memleak.

dev_pm_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 dev_pm_opp_enable to actually make it available.
	 opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false);
	 dev_pm_opp_put(opp);
	 /* dont operate on the pointer.. just do a sanity check.. */
	 if (IS_ERR(opp)) {
		pr_err("frequency not disabled!\n");
		/* trigger appropriate actions.. */
	 } else {
		dev_pm_opp_enable(dev,1000000000);
	 }

	NOTE: This is the only search function that operates on OPPs which are
	not available.

dev_pm_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;
	 opp = dev_pm_opp_find_freq_floor(dev, &freq);
	 dev_pm_opp_put(opp);

dev_pm_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;
	 opp = dev_pm_opp_find_freq_ceil(dev, &freq);
	 dev_pm_opp_put(opp);
	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 */
		opp = dev_pm_opp_find_freq_ceil(dev, &freq);
		dev_pm_opp_put(opp);
		if (!IS_ERR(opp))
			soc_switch_to_freq_voltage(freq);
		else
			/* do something when we can't 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.

dev_pm_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 */
		opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false);
		dev_pm_opp_put(opp);
		/* just error check */
		if (!IS_ERR(opp))
			ret = dev_pm_opp_enable(dev, 1000000000);
		else
			goto try_something_else;
	 }

dev_pm_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 */
		opp = dev_pm_opp_find_freq_exact(dev, 1000000000, true);
		dev_pm_opp_put(opp);
		/* just error check */
		if (!IS_ERR(opp))
			ret = dev_pm_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.

dev_pm_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 */
		opp = dev_pm_opp_find_freq_ceil(dev, &freq);
		v = dev_pm_opp_get_voltage(opp);
		dev_pm_opp_put(opp);
		if (v)
			regulator_set_voltage(.., v);
		/* do other things */
	 }

dev_pm_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;
		 max_opp = dev_pm_opp_find_freq_floor(dev,&max_freq);
		 requested_opp = dev_pm_opp_find_freq_ceil(dev,&freq);
		 if (!IS_ERR(max_opp) && !IS_ERR(requested_opp))
			r = soc_test_validity(max_opp, requested_opp);
		 dev_pm_opp_put(max_opp);
		 dev_pm_opp_put(requested_opp);
		/* do other things */
	 }
	 soc_test_validity(..)
	 {
		 if(dev_pm_opp_get_voltage(max_opp) < dev_pm_opp_get_voltage(requested_opp))
			 return -EINVAL;
		 if(dev_pm_opp_get_freq(max_opp) < dev_pm_opp_get_freq(requested_opp))
			 return -EINVAL;
		/* do things.. */
	 }

dev_pm_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 */
		num_available = dev_pm_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 = dev_pm_opp_find_freq_ceil(dev, &freq))) {
			speeds[i] = freq;
			freq++;
			i++;
			dev_pm_opp_put(opp);
		}

		soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available);
		/* Do other things */
	 }

6. 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 dev_pm_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 dev_pm_opp pointer should not be parsed or modified by the
	users. The defaults of for an instance is populated by dev_pm_opp_add, but the
	availability of the OPP can be modified by dev_pm_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:
            +-----+        /- dev_pm_opp_enable
dev_pm_opp_add --> | opp | <-------
  |         +-----+        \- dev_pm_opp_disable
  \-------> domain_info(device)

Search functions:
             /-- dev_pm_opp_find_freq_ceil  ---\   +-----+
domain_info<---- dev_pm_opp_find_freq_exact -----> | opp |
             \-- dev_pm_opp_find_freq_floor ---/   +-----+

Retrieval functions:
+-----+     /- dev_pm_opp_get_voltage
| opp | <---
+-----+     \- dev_pm_opp_get_freq

domain_info <- dev_pm_opp_get_opp_count
Commit	Line	Data
4b875810 NM	1	Operating Performance Points (OPP) Library
4b875810 NM	2	==========================================
e1f60b29 NM	3
	4	(C) 2009-2010 Nishanth Menon <nm@ti.com>, Texas Instruments Incorporated
	5
	6	Contents
	7	--------
	8	1. Introduction
	9	2. Initial OPP List Registration
	10	3. OPP Search Functions
	11	4. OPP Availability Control Functions
	12	5. OPP Data Retrieval Functions
a0dd7b79	13	6. Data Structures
e1f60b29 NM	14
	15	1. Introduction
	16	===============
4b875810 NM	17	1.1 What is an Operating Performance Point (OPP)?
4b875810 NM	18
e1f60b29 NM	19	Complex SoCs of today consists of a multiple sub-modules working in conjunction.
	20	In an operational system executing varied use cases, not all modules in the SoC
	21	need to function at their highest performing frequency all the time. To
	22	facilitate this, sub-modules in a SoC are grouped into domains, allowing some
4b875810 NM	23	domains to run at lower voltage and frequency while other domains run at
	24	voltage/frequency pairs that are higher.
	25
	26	The set of discrete tuples consisting of frequency and voltage pairs that
e1f60b29 NM	27	the device will support per domain are called Operating Performance Points or
	28	OPPs.
	29
4b875810 NM	30	As an example:
	31	Let us consider an MPU device which supports the following:
	32	{300MHz at minimum voltage of 1V}, {800MHz at minimum voltage of 1.2V},
	33	{1GHz at minimum voltage of 1.3V}
	34
	35	We can represent these as three OPPs as the following {Hz, uV} tuples:
	36	{300000000, 1000000}
	37	{800000000, 1200000}
	38	{1000000000, 1300000}
	39
	40	1.2 Operating Performance Points Library
	41
e1f60b29 NM	42	OPP library provides a set of helper functions to organize and query the OPP
e1f60b29 NM	43	information. The library is located in drivers/base/power/opp.c and the header
e4db1c74	44	is located in include/linux/pm_opp.h. OPP library can be enabled by enabling
e1f60b29 NM	45	CONFIG_PM_OPP from power management menuconfig menu. OPP library depends on
	46	CONFIG_PM as certain SoCs such as Texas Instrument's OMAP framework allows to
	47	optionally boot at a certain OPP without needing cpufreq.
	48
	49	Typical usage of the OPP library is as follows:
	50	(users) -> registers a set of default OPPs -> (library)
	51	SoC framework -> modifies on required cases certain OPPs -> OPP layer
	52	-> queries to search/retrieve information ->
	53
	54	OPP layer expects each domain to be represented by a unique device pointer. SoC
	55	framework registers a set of initial OPPs per device with the OPP layer. This
	56	list is expected to be an optimally small number typically around 5 per device.
	57	This initial list contains a set of OPPs that the framework expects to be safely
	58	enabled by default in the system.
	59
	60	Note on OPP Availability:
	61	------------------------
	62	As the system proceeds to operate, SoC framework may choose to make certain
	63	OPPs available or not available on each device based on various external
	64	factors. Example usage: Thermal management or other exceptional situations where
	65	SoC framework might choose to disable a higher frequency OPP to safely continue
	66	operations until that OPP could be re-enabled if possible.
	67
	68	OPP library facilitates this concept in it's implementation. The following
	69	operational functions operate only on available opps:
5d4879cd	70	opp_find_freq_{ceil, floor}, dev_pm_opp_get_voltage, dev_pm_opp_get_freq, dev_pm_opp_get_opp_count
e1f60b29	71
5d4879cd NM	72	dev_pm_opp_find_freq_exact is meant to be used to find the opp pointer which can then
5d4879cd NM	73	be used for dev_pm_opp_enable/disable functions to make an opp available as required.
e1f60b29 NM	74
e1f60b29 NM	75	WARNING: Users of OPP library should refresh their availability count using
5d4879cd	76	get_opp_count if dev_pm_opp_enable/disable functions are invoked for a device, the
e1f60b29 NM	77	exact mechanism to trigger these or the notification mechanism to other
	78	dependent subsystems such as cpufreq are left to the discretion of the SoC
	79	specific framework which uses the OPP library. Similar care needs to be taken
	80	care to refresh the cpufreq table in cases of these operations.
	81
e1f60b29 NM	82	2. Initial OPP List Registration
e1f60b29 NM	83	================================
5d4879cd	84	The SoC implementation calls dev_pm_opp_add function iteratively to add OPPs per
e1f60b29 NM	85	device. It is expected that the SoC framework will register the OPP entries
	86	optimally- typical numbers range to be less than 5. The list generated by
	87	registering the OPPs is maintained by OPP library throughout the device
	88	operation. The SoC framework can subsequently control the availability of the
5d4879cd	89	OPPs dynamically using the dev_pm_opp_enable / disable functions.
e1f60b29	90
5d4879cd	91	dev_pm_opp_add - Add a new OPP for a specific domain represented by the device pointer.
e1f60b29 NM	92	The OPP is defined using the frequency and voltage. Once added, the OPP
e1f60b29 NM	93	is assumed to be available and control of it's availability can be done
5d4879cd	94	with the dev_pm_opp_enable/disable functions. OPP library internally stores
e1f60b29 NM	95	and manages this information in the opp struct. This function may be
	96	used by SoC framework to define a optimal list as per the demands of
	97	SoC usage environment.
	98
	99	WARNING: Do not use this function in interrupt context.
	100
	101	Example:
	102	soc_pm_init()
	103	{
	104	/* Do things */
5d4879cd	105	r = dev_pm_opp_add(mpu_dev, 1000000, 900000);
e1f60b29 NM	106	if (!r) {
	107	pr_err("%s: unable to register mpu opp(%d)\n", r);
	108	goto no_cpufreq;
	109	}
	110	/* Do cpufreq things */
	111	no_cpufreq:
	112	/* Do remaining things */
	113	}
	114
	115	3. OPP Search Functions
	116	=======================
	117	High level framework such as cpufreq operates on frequencies. To map the
	118	frequency back to the corresponding OPP, OPP library provides handy functions
	119	to search the OPP list that OPP library internally manages. These search
	120	functions return the matching pointer representing the opp if a match is
	121	found, else returns error. These errors are expected to be handled by standard
	122	error checks such as IS_ERR() and appropriate actions taken by the caller.
	123
6185deaa VK	124	Callers of these functions shall call dev_pm_opp_put() after they have used the
	125	OPP. Otherwise the memory for the OPP will never get freed and result in
	126	memleak.
	127
5d4879cd	128	dev_pm_opp_find_freq_exact - Search for an OPP based on an exact frequency and
e1f60b29 NM	129	availability. This function is especially useful to enable an OPP which
	130	is not available by default.
	131	Example: In a case when SoC framework detects a situation where a
	132	higher frequency could be made available, it can use this function to
5d4879cd	133	find the OPP prior to call the dev_pm_opp_enable to actually make it available.
5d4879cd	134	opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false);
6185deaa	135	dev_pm_opp_put(opp);
e1f60b29 NM	136	/* dont operate on the pointer.. just do a sanity check.. */
	137	if (IS_ERR(opp)) {
	138	pr_err("frequency not disabled!\n");
	139	/* trigger appropriate actions.. */
	140	} else {
5d4879cd	141	dev_pm_opp_enable(dev,1000000000);
e1f60b29 NM	142	}
	143
	144	NOTE: This is the only search function that operates on OPPs which are
	145	not available.
	146
5d4879cd	147	dev_pm_opp_find_freq_floor - Search for an available OPP which is at most the
e1f60b29 NM	148	provided frequency. This function is useful while searching for a lesser
	149	match OR operating on OPP information in the order of decreasing
	150	frequency.
	151	Example: To find the highest opp for a device:
	152	freq = ULONG_MAX;
6185deaa VK	153	opp = dev_pm_opp_find_freq_floor(dev, &freq);
6185deaa VK	154	dev_pm_opp_put(opp);
e1f60b29	155
5d4879cd	156	dev_pm_opp_find_freq_ceil - Search for an available OPP which is at least the
e1f60b29 NM	157	provided frequency. This function is useful while searching for a
	158	higher match OR operating on OPP information in the order of increasing
	159	frequency.
	160	Example 1: To find the lowest opp for a device:
	161	freq = 0;
6185deaa VK	162	opp = dev_pm_opp_find_freq_ceil(dev, &freq);
6185deaa VK	163	dev_pm_opp_put(opp);
e1f60b29 NM	164	Example 2: A simplified implementation of a SoC cpufreq_driver->target:
	165	soc_cpufreq_target(..)
	166	{
	167	/* Do stuff like policy checks etc. */
	168	/* Find the best frequency match for the req */
5d4879cd	169	opp = dev_pm_opp_find_freq_ceil(dev, &freq);
6185deaa	170	dev_pm_opp_put(opp);
e1f60b29 NM	171	if (!IS_ERR(opp))
	172	soc_switch_to_freq_voltage(freq);
	173	else
25985edc	174	/* do something when we can't satisfy the req */
e1f60b29 NM	175	/* do other stuff */
	176	}
	177
	178	4. OPP Availability Control Functions
	179	=====================================
	180	A default OPP list registered with the OPP library may not cater to all possible
	181	situation. The OPP library provides a set of functions to modify the
	182	availability of a OPP within the OPP list. This allows SoC frameworks to have
	183	fine grained dynamic control of which sets of OPPs are operationally available.
	184	These functions are intended to temporarily remove an OPP in conditions such
	185	as thermal considerations (e.g. don't use OPPx until the temperature drops).
	186
	187	WARNING: Do not use these functions in interrupt context.
	188
5d4879cd	189	dev_pm_opp_enable - Make a OPP available for operation.
e1f60b29 NM	190	Example: Lets say that 1GHz OPP is to be made available only if the
	191	SoC temperature is lower than a certain threshold. The SoC framework
	192	implementation might choose to do something as follows:
	193	if (cur_temp < temp_low_thresh) {
	194	/* Enable 1GHz if it was disabled */
5d4879cd	195	opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false);
6185deaa	196	dev_pm_opp_put(opp);
e1f60b29 NM	197	/* just error check */
e1f60b29 NM	198	if (!IS_ERR(opp))
5d4879cd	199	ret = dev_pm_opp_enable(dev, 1000000000);
e1f60b29 NM	200	else
	201	goto try_something_else;
	202	}
	203
5d4879cd	204	dev_pm_opp_disable - Make an OPP to be not available for operation
e1f60b29 NM	205	Example: Lets say that 1GHz OPP is to be disabled if the temperature
	206	exceeds a threshold value. The SoC framework implementation might
	207	choose to do something as follows:
	208	if (cur_temp > temp_high_thresh) {
	209	/* Disable 1GHz if it was enabled */
5d4879cd	210	opp = dev_pm_opp_find_freq_exact(dev, 1000000000, true);
6185deaa	211	dev_pm_opp_put(opp);
e1f60b29 NM	212	/* just error check */
e1f60b29 NM	213	if (!IS_ERR(opp))
5d4879cd	214	ret = dev_pm_opp_disable(dev, 1000000000);
e1f60b29 NM	215	else
	216	goto try_something_else;
	217	}
	218
	219	5. OPP Data Retrieval Functions
	220	===============================
	221	Since OPP library abstracts away the OPP information, a set of functions to pull
	222	information from the OPP structure is necessary. Once an OPP pointer is
	223	retrieved using the search functions, the following functions can be used by SoC
	224	framework to retrieve the information represented inside the OPP layer.
	225
5d4879cd	226	dev_pm_opp_get_voltage - Retrieve the voltage represented by the opp pointer.
e1f60b29 NM	227	Example: At a cpufreq transition to a different frequency, SoC
	228	framework requires to set the voltage represented by the OPP using
	229	the regulator framework to the Power Management chip providing the
	230	voltage.
	231	soc_switch_to_freq_voltage(freq)
	232	{
	233	/* do things */
5d4879cd NM	234	opp = dev_pm_opp_find_freq_ceil(dev, &freq);
5d4879cd NM	235	v = dev_pm_opp_get_voltage(opp);
6185deaa	236	dev_pm_opp_put(opp);
e1f60b29 NM	237	if (v)
	238	regulator_set_voltage(.., v);
	239	/* do other things */
	240	}
	241
5d4879cd	242	dev_pm_opp_get_freq - Retrieve the freq represented by the opp pointer.
e1f60b29 NM	243	Example: Lets say the SoC framework uses a couple of helper functions
	244	we could pass opp pointers instead of doing additional parameters to
	245	handle quiet a bit of data parameters.
	246	soc_cpufreq_target(..)
	247	{
	248	/* do things.. */
	249	max_freq = ULONG_MAX;
5d4879cd NM	250	max_opp = dev_pm_opp_find_freq_floor(dev,&max_freq);
5d4879cd NM	251	requested_opp = dev_pm_opp_find_freq_ceil(dev,&freq);
e1f60b29 NM	252	if (!IS_ERR(max_opp) && !IS_ERR(requested_opp))
e1f60b29 NM	253	r = soc_test_validity(max_opp, requested_opp);
6185deaa VK	254	dev_pm_opp_put(max_opp);
6185deaa VK	255	dev_pm_opp_put(requested_opp);
e1f60b29 NM	256	/* do other things */
	257	}
	258	soc_test_validity(..)
	259	{
5d4879cd	260	if(dev_pm_opp_get_voltage(max_opp) < dev_pm_opp_get_voltage(requested_opp))
e1f60b29	261	return -EINVAL;
5d4879cd	262	if(dev_pm_opp_get_freq(max_opp) < dev_pm_opp_get_freq(requested_opp))
e1f60b29 NM	263	return -EINVAL;
	264	/* do things.. */
	265	}
	266
5d4879cd	267	dev_pm_opp_get_opp_count - Retrieve the number of available opps for a device
e1f60b29 NM	268	Example: Lets say a co-processor in the SoC needs to know the available
	269	frequencies in a table, the main processor can notify as following:
	270	soc_notify_coproc_available_frequencies()
	271	{
	272	/* Do things */
5d4879cd	273	num_available = dev_pm_opp_get_opp_count(dev);
e1f60b29 NM	274	speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL);
	275	/* populate the table in increasing order */
	276	freq = 0;
5d4879cd	277	while (!IS_ERR(opp = dev_pm_opp_find_freq_ceil(dev, &freq))) {
e1f60b29 NM	278	speeds[i] = freq;
	279	freq++;
	280	i++;
6185deaa	281	dev_pm_opp_put(opp);
e1f60b29	282	}
e1f60b29 NM	283
	284	soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available);
	285	/* Do other things */
	286	}
	287
a0dd7b79	288	6. Data Structures
e1f60b29 NM	289	==================
	290	Typically an SoC contains multiple voltage domains which are variable. Each
	291	domain is represented by a device pointer. The relationship to OPP can be
	292	represented as follows:
	293	SoC
	294	\|- device 1
	295	\| \|- opp 1 (availability, freq, voltage)
	296	\| \|- opp 2 ..
	297	... ...
	298	\| `- opp n ..
	299	\|- device 2
	300	...
	301	`- device m
	302
	303	OPP library maintains a internal list that the SoC framework populates and
	304	accessed by various functions as described above. However, the structures
	305	representing the actual OPPs and domains are internal to the OPP library itself
	306	to allow for suitable abstraction reusable across systems.
	307
47d43ba7	308	struct dev_pm_opp - The internal data structure of OPP library which is used to
e1f60b29 NM	309	represent an OPP. In addition to the freq, voltage, availability
	310	information, it also contains internal book keeping information required
	311	for the OPP library to operate on. Pointer to this structure is
	312	provided back to the users such as SoC framework to be used as a
	313	identifier for OPP in the interactions with OPP layer.
	314
47d43ba7	315	WARNING: The struct dev_pm_opp pointer should not be parsed or modified by the
5d4879cd NM	316	users. The defaults of for an instance is populated by dev_pm_opp_add, but the
5d4879cd NM	317	availability of the OPP can be modified by dev_pm_opp_enable/disable functions.
e1f60b29 NM	318
	319	struct device - This is used to identify a domain to the OPP layer. The
	320	nature of the device and it's implementation is left to the user of
	321	OPP library such as the SoC framework.
	322
	323	Overall, in a simplistic view, the data structure operations is represented as
	324	following:
	325
	326	Initialization / modification:
5d4879cd NM	327	+-----+ /- dev_pm_opp_enable
	328	dev_pm_opp_add --> \| opp \| <-------
	329	\| +-----+ \- dev_pm_opp_disable
e1f60b29 NM	330	\-------> domain_info(device)
	331
	332	Search functions:
5d4879cd NM	333	/-- dev_pm_opp_find_freq_ceil ---\ +-----+
	334	domain_info<---- dev_pm_opp_find_freq_exact -----> \| opp \|
	335	\-- dev_pm_opp_find_freq_floor ---/ +-----+
e1f60b29 NM	336
e1f60b29 NM	337	Retrieval functions:
5d4879cd	338	+-----+ /- dev_pm_opp_get_voltage
e1f60b29	339	\| opp \| <---
5d4879cd	340	+-----+ \- dev_pm_opp_get_freq
e1f60b29	341
5d4879cd	342	domain_info <- dev_pm_opp_get_opp_count