docs: power: convert docs to ReST and rename to *.rst

Convert the PM documents to ReST, in order to allow them to
build with Sphinx.

The conversion is actually:
  - add blank lines and indentation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>

1 files changed, 379 insertions, 0 deletions

diff --git a/Documentation/power/opp.rst b/Documentation/power/opp.rst
new file mode 100644
index 000000000000..b3cf1def9dee
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+==========================================
+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