Documentation/cpu-freq/cpu-drivers.rst

1 .. SPDX-License-Identifier: GPL-2.0
10 	- Dominik Brodowski  <linux@brodo.de>
11 	- Rafael J. Wysocki <rafael.j.wysocki@intel.com>
12 	- Viresh Kumar <viresh.kumar@linaro.org>
18    1.2  Per-CPU Initialization
31 So, you just got a brand-new CPU / chipset with datasheets and want to
37 ------------------
46  .name - The name of this driver.
48  .init - A pointer to the per-policy initialization function.
50  .verify - A pointer to a "verification" function.
52  .setpolicy _or_ .fast_switch _or_ .target _or_ .target_index - See
57  .flags - Hints for the cpufreq core.
59  .driver_data - cpufreq driver specific data.
61  .resolve_freq - Returns the most appropriate frequency for a target
64  .get_intermediate and target_intermediate - Used to switch to stable
67  .get - Returns current frequency of the CPU.
69  .bios_limit - Returns HW/BIOS max frequency limitations for the CPU.
71  .exit - A pointer to a per-policy cleanup function called during
74  .stop_cpu - A pointer to a per-policy stop function called during
77  .suspend - A pointer to a per-policy suspend function which is called
81  .resume - A pointer to a per-policy resume function which is called
84  .ready - A pointer to a per-policy ready function which is called after
87  .attr - A pointer to a NULL-terminated list of "struct freq_attr" which
90  .boost_enabled - If set, boost frequencies are enabled.
92  .set_boost - A pointer to a per-policy function to enable/disable boost
96 1.2 Per-CPU Initialization
97 --------------------------
100 cpufreq driver registers itself, the per-policy initialization function
110 +-----------------------------------+--------------------------------------+
111 |policy->cpuinfo.min_freq _and_	    |					   |
112 |policy->cpuinfo.max_freq	    | the minimum and maximum frequency	   |
115 +-----------------------------------+--------------------------------------+
116 |policy->cpuinfo.transition_latency | the time it takes on this CPU to	   |
120 +-----------------------------------+--------------------------------------+
121 |policy->cur			    | The current operating frequency of   |
123 +-----------------------------------+--------------------------------------+
124 |policy->min,			    |					   |
125 |policy->max,			    |					   |
126 |policy->policy and, if necessary,  |					   |
127 |policy->governor		    | must contain the "default policy" for|
133 +-----------------------------------+--------------------------------------+
134 |policy->cpus			    | Update this with the masks of the	   |
138 +-----------------------------------+--------------------------------------+
140 For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the
146 ----------
156 range) is within policy->min and policy->max. If necessary, increase
157 policy->max first, and only if this is no solution, decrease policy->min.
161 -------------------------------------------------------
165 these, you use the ->target(), ->target_index() or ->fast_switch()
169 limits on their own. These shall use the ->setpolicy() callback.
173 ------------------------
181 It should always restore to earlier frequency (i.e. policy->restore_freq) in
185 ----------
192 - keep close to "target_freq"
193 - policy->min <= new_freq <= policy->max (THIS MUST BE VALID!!!)
194 - if relation==CPUFREQ_REL_L, try to select a new_freq higher than or equal
196 - if relation==CPUFREQ_REL_H, try to select a new_freq lower than or equal
199 Here again the frequency table helper might assist you - see section 2
203 ----------------
215 -------------
218 argument. You need to set the lower limit of the in-processor or
219 in-chipset dynamic frequency switching to policy->min, the upper limit
220 to policy->max, and -if supported- select a performance-oriented
221 setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a
222 powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check
226 --------------------------------------------
238 directly call ->target_index().
240 NOTE: ->target_index() should restore to policy->restore_freq in case of
260 valid pointer in its policy->freq_table field.
263 frequency is within policy->min and policy->max, and all other criteria
264 are met. This is helpful for the ->verify call.
267 helper for the ->target stage. Just pass the values to this function,
273 cpufreq_for_each_entry(pos, table) - iterates over all entries of frequency
276 cpufreq_for_each_valid_entry(pos, table) - iterates over all entries,
278 Use arguments "pos" - a ``cpufreq_frequency_table *`` as a loop cursor and
279 "table" - the ``cpufreq_frequency_table *`` you want to iterate over.
287 		pos->frequency = ...