mirror of
https://github.com/torvalds/linux.git
synced 2024-12-05 10:32:35 +00:00
99f381d354
cpufreq table allocated by opp_init_cpufreq_table is better freed by OPP layer itself. This allows future modifications to the table handling to be transparent to the users. Signed-off-by: Nishanth Menon <nm@ti.com> Acked-by: Kevin Hilman <khilman@ti.com> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
381 lines
15 KiB
Plaintext
381 lines
15 KiB
Plaintext
*=============*
|
|
* 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
|