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diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt deleted file mode 100644 index 3035d00757a..00000000000 --- a/Documentation/power/opp.txt +++ /dev/null @@ -1,380 +0,0 @@ -*=============* -* 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 |