UM0851 datasheet(231/245 Pages) STMICROELECTRONICS

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UM0851

Power management section

Doc ID 16604 Rev 2

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10.3.3 CPU freq framework API

The architecture specific CPUfreq driver registers into the CPUfreq core via the following

structure.

struct cpufreq_driver {

struct module*owner;

char

name[CPUFREQ_NAME_LEN];

flags;

int

(*init)(struct cpufreq_policy *policy);

int

(*verify)(struct cpufreq_policy *policy);

int

(*setpolicy)(struct cpufreq_policy *policy);

int

(*target)(struct cpufreq_policy *policy,

unsigned int target_freq,

unsigned int relation);

/* should be defined, if possible */

unsigned int(*get)(unsigned int cpu);

/* optional */

unsigned int (*getavg)(unsigned int cpu);

int

(*exit)(struct cpufreq_policy *policy);

int

(*suspend)(struct cpufreq_policy *policy, pm_message_t pmsg);

int

(*resume)(struct cpufreq_policy *policy);

struct freq_attr

**attr;

};

Above defined structure provide few call back functions that have to be added in the SPEAr

architecture code to provide the transitions into the new frequency for the CPU as requested

by the CPUfreq framework.

●

init (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. The driver provides in the "Policy" related information to

the CPUfreq core. This includes the CPU operating/min/max frequency, and

information related to the governor that the core should use for switching the frequency.

The policy related information is captured in the following data structure by the kernel:

struct cpufreq_policy {

cpumask_t

cpus;

/* CPUs requiring sw coordination */

cpumask_t

related_cpus; /* CPUs with any coordination */

unsigned int

shared_type; /* ANY or ALL affected CPUs should set

cpufreq

unsigned int

cpu;

/* cpu nr of registered CPU */

struct cpufreq_cpuinfo

cpuinfo;/* see above */

unsigned int

min;

/* in kHz */

unsigned int

max;

/* in kHz */

unsigned int

cur;

/* in kHz, only needed if cpufreq governors are used

unsigned int

policy; /* see above */

struct cpufreq_governor *governor;

struct work_struct

update; /* if update_policy() needs to be called, but you're

in IRQ context */

struct cpufreq_real_policy

user_policy;

struct kobject

kobj;

struct completion

kobj_unregister;

●

Verify: When the user decides that a new policy (consisting of "policy, governor, min,

max") shall be set, this policy must be validated so that incompatible values can be

corrected.

●

Target: The target call has three arguments: struct cpufreq_policy *policy, unsigned int

target_frequency, unsigned int relation. The CPUfreq driver sets the new frequency

when called here. Apart from the change in frequency the driver must also notify into

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