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-*=============*
-* 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 ->
-
-Architectures that provide a SoC framework for OPP should select ARCH_HAS_OPP
-to make the OPP layer available.
-
-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 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.
-
-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.
-
-opp_free_cpufreq_table - Free up the table allocated by opp_init_cpufreq_table
-
-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