diff options
Diffstat (limited to 'Documentation/cpu-freq')
| -rw-r--r-- | Documentation/cpu-freq/core.rst | 113 | ||||
| -rw-r--r-- | Documentation/cpu-freq/cpu-drivers.rst | 292 | ||||
| -rw-r--r-- | Documentation/cpu-freq/cpufreq-stats.rst | 136 | ||||
| -rw-r--r-- | Documentation/cpu-freq/index.rst | 39 |
4 files changed, 580 insertions, 0 deletions
diff --git a/Documentation/cpu-freq/core.rst b/Documentation/cpu-freq/core.rst new file mode 100644 index 000000000..33cb90bd1 --- /dev/null +++ b/Documentation/cpu-freq/core.rst @@ -0,0 +1,113 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================================= +General description of the CPUFreq core and CPUFreq notifiers +============================================================= + +Authors: + - Dominik Brodowski <linux@brodo.de> + - David Kimdon <dwhedon@debian.org> + - Rafael J. Wysocki <rafael.j.wysocki@intel.com> + - Viresh Kumar <viresh.kumar@linaro.org> + +.. Contents: + + 1. CPUFreq core and interfaces + 2. CPUFreq notifiers + 3. CPUFreq Table Generation with Operating Performance Point (OPP) + +1. General Information +====================== + +The CPUFreq core code is located in drivers/cpufreq/cpufreq.c. This +cpufreq code offers a standardized interface for the CPUFreq +architecture drivers (those pieces of code that do actual +frequency transitions), as well as to "notifiers". These are device +drivers or other part of the kernel that need to be informed of +policy changes (ex. thermal modules like ACPI) or of all +frequency changes (ex. timing code) or even need to force certain +speed limits (like LCD drivers on ARM architecture). Additionally, the +kernel "constant" loops_per_jiffy is updated on frequency changes +here. + +Reference counting of the cpufreq policies is done by cpufreq_cpu_get +and cpufreq_cpu_put, which make sure that the cpufreq driver is +correctly registered with the core, and will not be unloaded until +cpufreq_put_cpu is called. That also ensures that the respective cpufreq +policy doesn't get freed while being used. + +2. CPUFreq notifiers +==================== + +CPUFreq notifiers conform to the standard kernel notifier interface. +See linux/include/linux/notifier.h for details on notifiers. + +There are two different CPUFreq notifiers - policy notifiers and +transition notifiers. + + +2.1 CPUFreq policy notifiers +---------------------------- + +These are notified when a new policy is created or removed. + +The phase is specified in the second argument to the notifier. The phase is +CPUFREQ_CREATE_POLICY when the policy is first created and it is +CPUFREQ_REMOVE_POLICY when the policy is removed. + +The third argument, a ``void *pointer``, points to a struct cpufreq_policy +consisting of several values, including min, max (the lower and upper +frequencies (in kHz) of the new policy). + + +2.2 CPUFreq transition notifiers +-------------------------------- + +These are notified twice for each online CPU in the policy, when the +CPUfreq driver switches the CPU core frequency and this change has no +any external implications. + +The second argument specifies the phase - CPUFREQ_PRECHANGE or +CPUFREQ_POSTCHANGE. + +The third argument is a struct cpufreq_freqs with the following +values: + +===== =========================== +cpu number of the affected CPU +old old frequency +new new frequency +flags flags of the cpufreq driver +===== =========================== + +3. CPUFreq Table Generation with Operating Performance Point (OPP) +================================================================== +For details about OPP, see Documentation/power/opp.rst + +dev_pm_opp_init_cpufreq_table - + 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 = dev_pm_opp_init_cpufreq_table(dev, &freq_table); + if (!r) + policy->freq_table = freq_table; + /* Do other things */ + } + + .. note:: + + This function is available only if CONFIG_CPU_FREQ is enabled in + addition to CONFIG_PM_OPP. + +dev_pm_opp_free_cpufreq_table + Free up the table allocated by dev_pm_opp_init_cpufreq_table diff --git a/Documentation/cpu-freq/cpu-drivers.rst b/Documentation/cpu-freq/cpu-drivers.rst new file mode 100644 index 000000000..a697278ce --- /dev/null +++ b/Documentation/cpu-freq/cpu-drivers.rst @@ -0,0 +1,292 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============================================== +How to Implement a new CPUFreq Processor Driver +=============================================== + +Authors: + + + - Dominik Brodowski <linux@brodo.de> + - Rafael J. Wysocki <rafael.j.wysocki@intel.com> + - Viresh Kumar <viresh.kumar@linaro.org> + +.. Contents + + 1. What To Do? + 1.1 Initialization + 1.2 Per-CPU Initialization + 1.3 verify + 1.4 target/target_index or setpolicy? + 1.5 target/target_index + 1.6 setpolicy + 1.7 get_intermediate and target_intermediate + 2. Frequency Table Helpers + + + +1. What To Do? +============== + +So, you just got a brand-new CPU / chipset with datasheets and want to +add cpufreq support for this CPU / chipset? Great. Here are some hints +on what is necessary: + + +1.1 Initialization +------------------ + +First of all, in an __initcall level 7 (module_init()) or later +function check whether this kernel runs on the right CPU and the right +chipset. If so, register a struct cpufreq_driver with the CPUfreq core +using cpufreq_register_driver() + +What shall this struct cpufreq_driver contain? + + .name - The name of this driver. + + .init - A pointer to the per-policy initialization function. + + .verify - A pointer to a "verification" function. + + .setpolicy _or_ .fast_switch _or_ .target _or_ .target_index - See + below on the differences. + +And optionally + + .flags - Hints for the cpufreq core. + + .driver_data - cpufreq driver specific data. + + .resolve_freq - Returns the most appropriate frequency for a target + frequency. Doesn't change the frequency though. + + .get_intermediate and target_intermediate - Used to switch to stable + frequency while changing CPU frequency. + + .get - Returns current frequency of the CPU. + + .bios_limit - Returns HW/BIOS max frequency limitations for the CPU. + + .exit - A pointer to a per-policy cleanup function called during + CPU_POST_DEAD phase of cpu hotplug process. + + .stop_cpu - A pointer to a per-policy stop function called during + CPU_DOWN_PREPARE phase of cpu hotplug process. + + .suspend - A pointer to a per-policy suspend function which is called + with interrupts disabled and _after_ the governor is stopped for the + policy. + + .resume - A pointer to a per-policy resume function which is called + with interrupts disabled and _before_ the governor is started again. + + .ready - A pointer to a per-policy ready function which is called after + the policy is fully initialized. + + .attr - A pointer to a NULL-terminated list of "struct freq_attr" which + allow to export values to sysfs. + + .boost_enabled - If set, boost frequencies are enabled. + + .set_boost - A pointer to a per-policy function to enable/disable boost + frequencies. + + +1.2 Per-CPU Initialization +-------------------------- + +Whenever a new CPU is registered with the device model, or after the +cpufreq driver registers itself, the per-policy initialization function +cpufreq_driver.init is called if no cpufreq policy existed for the CPU. +Note that the .init() and .exit() routines are called only once for the +policy and not for each CPU managed by the policy. It takes a ``struct +cpufreq_policy *policy`` as argument. What to do now? + +If necessary, activate the CPUfreq support on your CPU. + +Then, the driver must fill in the following values: + ++-----------------------------------+--------------------------------------+ +|policy->cpuinfo.min_freq _and_ | | +|policy->cpuinfo.max_freq | the minimum and maximum frequency | +| | (in kHz) which is supported by | +| | this CPU | ++-----------------------------------+--------------------------------------+ +|policy->cpuinfo.transition_latency | the time it takes on this CPU to | +| | switch between two frequencies in | +| | nanoseconds (if appropriate, else | +| | specify CPUFREQ_ETERNAL) | ++-----------------------------------+--------------------------------------+ +|policy->cur | The current operating frequency of | +| | this CPU (if appropriate) | ++-----------------------------------+--------------------------------------+ +|policy->min, | | +|policy->max, | | +|policy->policy and, if necessary, | | +|policy->governor | must contain the "default policy" for| +| | this CPU. A few moments later, | +| | cpufreq_driver.verify and either | +| | cpufreq_driver.setpolicy or | +| | cpufreq_driver.target/target_index is| +| | called with these values. | ++-----------------------------------+--------------------------------------+ +|policy->cpus | Update this with the masks of the | +| | (online + offline) CPUs that do DVFS | +| | along with this CPU (i.e. that share| +| | clock/voltage rails with it). | ++-----------------------------------+--------------------------------------+ + +For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the +frequency table helpers might be helpful. See the section 2 for more information +on them. + + +1.3 verify +---------- + +When the user decides a new policy (consisting of +"policy,governor,min,max") shall be set, this policy must be validated +so that incompatible values can be corrected. For verifying these +values cpufreq_verify_within_limits(``struct cpufreq_policy *policy``, +``unsigned int min_freq``, ``unsigned int max_freq``) function might be helpful. +See section 2 for details on frequency table helpers. + +You need to make sure that at least one valid frequency (or operating +range) is within policy->min and policy->max. If necessary, increase +policy->max first, and only if this is no solution, decrease policy->min. + + +1.4 target or target_index or setpolicy or fast_switch? +------------------------------------------------------- + +Most cpufreq drivers or even most cpu frequency scaling algorithms +only allow the CPU frequency to be set to predefined fixed values. For +these, you use the ->target(), ->target_index() or ->fast_switch() +callbacks. + +Some cpufreq capable processors switch the frequency between certain +limits on their own. These shall use the ->setpolicy() callback. + + +1.5. target/target_index +------------------------ + +The target_index call has two arguments: ``struct cpufreq_policy *policy``, +and ``unsigned int`` index (into the exposed frequency table). + +The CPUfreq driver must set the new frequency when called here. The +actual frequency must be determined by freq_table[index].frequency. + +It should always restore to earlier frequency (i.e. policy->restore_freq) in +case of errors, even if we switched to intermediate frequency earlier. + +Deprecated +---------- +The target call has three arguments: ``struct cpufreq_policy *policy``, +unsigned int target_frequency, unsigned int relation. + +The CPUfreq driver must set the new frequency when called here. The +actual frequency must be determined using the following rules: + +- keep close to "target_freq" +- policy->min <= new_freq <= policy->max (THIS MUST BE VALID!!!) +- if relation==CPUFREQ_REL_L, try to select a new_freq higher than or equal + target_freq. ("L for lowest, but no lower than") +- if relation==CPUFREQ_REL_H, try to select a new_freq lower than or equal + target_freq. ("H for highest, but no higher than") + +Here again the frequency table helper might assist you - see section 2 +for details. + +1.6. fast_switch +---------------- + +This function is used for frequency switching from scheduler's context. +Not all drivers are expected to implement it, as sleeping from within +this callback isn't allowed. This callback must be highly optimized to +do switching as fast as possible. + +This function has two arguments: ``struct cpufreq_policy *policy`` and +``unsigned int target_frequency``. + + +1.7 setpolicy +------------- + +The setpolicy call only takes a ``struct cpufreq_policy *policy`` as +argument. You need to set the lower limit of the in-processor or +in-chipset dynamic frequency switching to policy->min, the upper limit +to policy->max, and -if supported- select a performance-oriented +setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a +powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check +the reference implementation in drivers/cpufreq/longrun.c + +1.8 get_intermediate and target_intermediate +-------------------------------------------- + +Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset. + +get_intermediate should return a stable intermediate frequency platform wants to +switch to, and target_intermediate() should set CPU to that frequency, before +jumping to the frequency corresponding to 'index'. Core will take care of +sending notifications and driver doesn't have to handle them in +target_intermediate() or target_index(). + +Drivers can return '0' from get_intermediate() in case they don't wish to switch +to intermediate frequency for some target frequency. In that case core will +directly call ->target_index(). + +NOTE: ->target_index() should restore to policy->restore_freq in case of +failures as core would send notifications for that. + + +2. Frequency Table Helpers +========================== + +As most cpufreq processors only allow for being set to a few specific +frequencies, a "frequency table" with some functions might assist in +some work of the processor driver. Such a "frequency table" consists of +an array of struct cpufreq_frequency_table entries, with driver specific +values in "driver_data", the corresponding frequency in "frequency" and +flags set. At the end of the table, you need to add a +cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END. +And if you want to skip one entry in the table, set the frequency to +CPUFREQ_ENTRY_INVALID. The entries don't need to be in sorted in any +particular order, but if they are cpufreq core will do DVFS a bit +quickly for them as search for best match is faster. + +The cpufreq table is verified automatically by the core if the policy contains a +valid pointer in its policy->freq_table field. + +cpufreq_frequency_table_verify() assures that at least one valid +frequency is within policy->min and policy->max, and all other criteria +are met. This is helpful for the ->verify call. + +cpufreq_frequency_table_target() is the corresponding frequency table +helper for the ->target stage. Just pass the values to this function, +and this function returns the of the frequency table entry which +contains the frequency the CPU shall be set to. + +The following macros can be used as iterators over cpufreq_frequency_table: + +cpufreq_for_each_entry(pos, table) - iterates over all entries of frequency +table. + +cpufreq_for_each_valid_entry(pos, table) - iterates over all entries, +excluding CPUFREQ_ENTRY_INVALID frequencies. +Use arguments "pos" - a ``cpufreq_frequency_table *`` as a loop cursor and +"table" - the ``cpufreq_frequency_table *`` you want to iterate over. + +For example:: + + struct cpufreq_frequency_table *pos, *driver_freq_table; + + cpufreq_for_each_entry(pos, driver_freq_table) { + /* Do something with pos */ + pos->frequency = ... + } + +If you need to work with the position of pos within driver_freq_table, +do not subtract the pointers, as it is quite costly. Instead, use the +macros cpufreq_for_each_entry_idx() and cpufreq_for_each_valid_entry_idx(). diff --git a/Documentation/cpu-freq/cpufreq-stats.rst b/Documentation/cpu-freq/cpufreq-stats.rst new file mode 100644 index 000000000..9ad695b1c --- /dev/null +++ b/Documentation/cpu-freq/cpufreq-stats.rst @@ -0,0 +1,136 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================== +General Description of sysfs CPUFreq Stats +========================================== + +information for users + + +Author: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> + +.. Contents + + 1. Introduction + 2. Statistics Provided (with example) + 3. Configuring cpufreq-stats + + +1. Introduction +=============== + +cpufreq-stats is a driver that provides CPU frequency statistics for each CPU. +These statistics are provided in /sysfs as a bunch of read_only interfaces. This +interface (when configured) will appear in a separate directory under cpufreq +in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU. +Various statistics will form read_only files under this directory. + +This driver is designed to be independent of any particular cpufreq_driver +that may be running on your CPU. So, it will work with any cpufreq_driver. + + +2. Statistics Provided (with example) +===================================== + +cpufreq stats provides following statistics (explained in detail below). + +- time_in_state +- total_trans +- trans_table + +All the statistics will be from the time the stats driver has been inserted +(or the time the stats were reset) to the time when a read of a particular +statistic is done. Obviously, stats driver will not have any information +about the frequency transitions before the stats driver insertion. + +:: + + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l + total 0 + drwxr-xr-x 2 root root 0 May 14 16:06 . + drwxr-xr-x 3 root root 0 May 14 15:58 .. + --w------- 1 root root 4096 May 14 16:06 reset + -r--r--r-- 1 root root 4096 May 14 16:06 time_in_state + -r--r--r-- 1 root root 4096 May 14 16:06 total_trans + -r--r--r-- 1 root root 4096 May 14 16:06 trans_table + +- **reset** + +Write-only attribute that can be used to reset the stat counters. This can be +useful for evaluating system behaviour under different governors without the +need for a reboot. + +- **time_in_state** + +This gives the amount of time spent in each of the frequencies supported by +this CPU. The cat output will have "<frequency> <time>" pair in each line, which +will mean this CPU spent <time> usertime units of time at <frequency>. Output +will have one line for each of the supported frequencies. usertime units here +is 10mS (similar to other time exported in /proc). + +:: + + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state + 3600000 2089 + 3400000 136 + 3200000 34 + 3000000 67 + 2800000 172488 + + +- **total_trans** + +This gives the total number of frequency transitions on this CPU. The cat +output will have a single count which is the total number of frequency +transitions. + +:: + + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans + 20 + +- **trans_table** + +This will give a fine grained information about all the CPU frequency +transitions. The cat output here is a two dimensional matrix, where an entry +<i,j> (row i, column j) represents the count of number of transitions from +Freq_i to Freq_j. Freq_i rows and Freq_j columns follow the sorting order in +which the driver has provided the frequency table initially to the cpufreq core +and so can be sorted (ascending or descending) or unsorted. The output here +also contains the actual freq values for each row and column for better +readability. + +If the transition table is bigger than PAGE_SIZE, reading this will +return an -EFBIG error. + +:: + + <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table + From : To + : 3600000 3400000 3200000 3000000 2800000 + 3600000: 0 5 0 0 0 + 3400000: 4 0 2 0 0 + 3200000: 0 1 0 2 0 + 3000000: 0 0 1 0 3 + 2800000: 0 0 0 2 0 + +3. Configuring cpufreq-stats +============================ + +To configure cpufreq-stats in your kernel:: + + Config Main Menu + Power management options (ACPI, APM) ---> + CPU Frequency scaling ---> + [*] CPU Frequency scaling + [*] CPU frequency translation statistics + + +"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure +cpufreq-stats. + +"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the +statistics which includes time_in_state, total_trans and trans_table. + +Once this option is enabled and your CPU supports cpufrequency, you +will be able to see the CPU frequency statistics in /sysfs. diff --git a/Documentation/cpu-freq/index.rst b/Documentation/cpu-freq/index.rst new file mode 100644 index 000000000..aba7831ab --- /dev/null +++ b/Documentation/cpu-freq/index.rst @@ -0,0 +1,39 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================================================== +Linux CPUFreq - CPU frequency and voltage scaling code in the Linux(TM) kernel +============================================================================== + +Author: Dominik Brodowski <linux@brodo.de> + + Clock scaling allows you to change the clock speed of the CPUs on the + fly. This is a nice method to save battery power, because the lower + the clock speed, the less power the CPU consumes. + + +.. toctree:: + :maxdepth: 1 + + core + cpu-drivers + cpufreq-stats + +Mailing List +------------ +There is a CPU frequency changing CVS commit and general list where +you can report bugs, problems or submit patches. To post a message, +send an email to linux-pm@vger.kernel.org. + +Links +----- +the FTP archives: +* ftp://ftp.linux.org.uk/pub/linux/cpufreq/ + +how to access the CVS repository: +* http://cvs.arm.linux.org.uk/ + +the CPUFreq Mailing list: +* http://vger.kernel.org/vger-lists.html#linux-pm + +Clock and voltage scaling for the SA-1100: +* http://www.lartmaker.nl/projects/scaling |