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Diffstat (limited to 'Documentation/cpu-freq/cpu-drivers.txt')
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diff --git a/Documentation/cpu-freq/cpu-drivers.txt b/Documentation/cpu-freq/cpu-drivers.txt deleted file mode 100644 index 19fa98e07bf7..000000000000 --- a/Documentation/cpu-freq/cpu-drivers.txt +++ /dev/null @@ -1,217 +0,0 @@ - CPU frequency and voltage scaling code in the Linux(TM) kernel - - - L i n u x C P U F r e q - - C P U D r i v e r s - - - information for developers - - - - 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. - - -Contents: ---------- -1. What To Do? -1.1 Initialization -1.2 Per-CPU Initialization -1.3 verify -1.4 target or setpolicy? -1.5 target -1.6 setpolicy -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? - -cpufreq_driver.name - The name of this driver. - -cpufreq_driver.owner - THIS_MODULE; - -cpufreq_driver.init - A pointer to the per-CPU initialization - function. - -cpufreq_driver.verify - A pointer to a "verification" function. - -cpufreq_driver.setpolicy _or_ -cpufreq_driver.target - See below on the differences. - -And optionally - -cpufreq_driver.exit - A pointer to a per-CPU cleanup function. - -cpufreq_driver.resume - A pointer to a per-CPU resume function - which is called with interrupts disabled - and _before_ the pre-suspend frequency - and/or policy is restored by a call to - ->target or ->setpolicy. - -cpufreq_driver.attr - A pointer to a NULL-terminated list of - "struct freq_attr" which allow to - export values to sysfs. - - -1.2 Per-CPU Initialization --------------------------- - -Whenever a new CPU is registered with the device model, or after the -cpufreq driver registers itself, the per-CPU initialization function -cpufreq_driver.init is called. 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 is called with - these values. - -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. - -SMP systems normally have same clock source for a group of cpus. For these the -.init() would be called only once for the first online cpu. Here the .init() -routine must initialize policy->cpus with mask of all possible cpus (Online + -Offline) that share the clock. Then the core would copy this mask onto -policy->related_cpus and will reset policy->cpus to carry only online cpus. - - -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, a frequency table helper and/or the -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 setpolicy? ----------------------------- - -Most cpufreq drivers or even most cpu frequency scaling algorithms -only allow the CPU to be set to one frequency. For these, you use the -->target call. - -Some cpufreq-capable processors switch the frequency between certain -limits on their own. These shall use the ->setpolicy call - - -1.4. target -------------- - -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. - - -1.5 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 - - - -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 any value in -"driver_data" you want to use, and the corresponding frequency in -"frequency". 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 ascending -order. - -By calling cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy, - struct cpufreq_frequency_table *table); -the cpuinfo.min_freq and cpuinfo.max_freq values are detected, and -policy->min and policy->max are set to the same values. This is -helpful for the per-CPU initialization stage. - -int cpufreq_frequency_table_verify(struct cpufreq_policy *policy, - struct cpufreq_frequency_table *table); -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. - -int cpufreq_frequency_table_target(struct cpufreq_policy *policy, - struct cpufreq_frequency_table *table, - unsigned int target_freq, - unsigned int relation, - unsigned int *index); - -is the corresponding frequency table helper for the ->target -stage. Just pass the values to this function, and the unsigned int -index returns the number of the frequency table entry which contains -the frequency the CPU shall be set to. |