2 files changed, 377 insertions, 0 deletions

diff --git a/Documentation/power/00-INDEX b/Documentation/power/00-INDEX
index fb742c213c9e..45e9d4a91284 100644
--- a/Documentation/power/00-INDEX
+++ b/Documentation/power/00-INDEX
@@ -14,6 +14,8 @@ interface.txt
         - Power management user interface in /sys/power
 notifiers.txt
         - Registering suspend notifiers in device drivers
+opp.txt
+        - Operating Performance Point library
 pci.txt
         - How the PCI Subsystem Does Power Management
 pm_qos_interface.txt
diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt
new file mode 100644
index 000000000000..44d87ad3cea9
--- /dev/null
+++ b/Documentation/power/opp.txt
@@ -0,0 +1,375 @@
+*=============*
+* 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