目录

1、注册接口：

2、去注册接口：

3、使用样例

4、软件处理

4.1 对cpufreq_transition_notifier_list的处理

4.2 对cpufreq_policy_notifier_list的处理

本章节主要介绍cpufreq中的通知链实现，在调频策略以及频率变化时来通知对该事件敏感的模块，各个模块可以通过注册和去注册接口来加入到通知链中。

1、注册接口：

   
    

     
 
      
 
       
 
      
 
      
 
       
 
        /** 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * cpufreq_register_notifier - Register a notifier with cpufreq. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * @nb: notifier function to register. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * @list: CPUFREQ_TRANSITION_NOTIFIER or CPUFREQ_POLICY_NOTIFIER. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * Add a notifier to one of two lists: either a list of notifiers that run on 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * clock rate changes (once before and once after every transition), or a list 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * of notifiers that ron on cpufreq policy changes. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * This function may sleep and it has the same return values as 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * blocking_notifier_chain_register(). 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         */ 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        int ret; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        if ( 
        cpufreq_disabled()) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        return -EINVAL; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        switch (list) { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        case CPUFREQ_TRANSITION_NOTIFIER: 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        mutex_lock(&cpufreq_fast_switch_lock); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        if (cpufreq_fast_switch_count > 
        0) { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                   
        mutex_unlock(&cpufreq_fast_switch_lock); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                   
        return -EBUSY; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     } 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     ret = 
        srcu_notifier_chain_register( 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                                 &cpufreq_transition_notifier_list, nb); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        if (!ret) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                   cpufreq_fast_switch_count--; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        mutex_unlock(&cpufreq_fast_switch_lock); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        break; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        case CPUFREQ_POLICY_NOTIFIER: 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     ret = 
        blocking_notifier_chain_register( 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                                 &cpufreq_policy_notifier_list, nb); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        break; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        default: 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     ret = -EINVAL; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       } 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        return ret; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         } 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        EXPORT_SYMBOL(cpufreq_register_notifier); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
    
   
    

    
     
   
    
   
    

CPUFREQ_TRANSITION_NOTIFIER：对频率变化敏感，注册进来的模块添加到cpufreq_transition_notifier_list链表中进行维护及后续操作，模块在回调中进行处理时，可以通过CPUFREQ_PRECHANGE和CPUFREQ_POSTCHANGE来区分是在频率变化前做动作还是在变化后做动作。

CPUFREQ_POLICY_NOTIFIER：对策略变化敏感，注册进来的模块，添加到cpufreq_policy_notifier_list链表中进行维护及后续操作，模块在回调中进行处理时，可以通过CPUFREQ_CREATE_POLICY和CPUFREQ_REMOVE_POLICY来区分是在策略变化前做动作还是在变化后做动作。

2、去注册接口：

   
    

     
 
      
 
       
 
      
 
      
 
       
 
        /** 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * cpufreq_unregister_notifier - Unregister a notifier from cpufreq. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * @nb: notifier block to be unregistered. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * @list: CPUFREQ_TRANSITION_NOTIFIER or CPUFREQ_POLICY_NOTIFIER. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * Remove a notifier from one of the cpufreq notifier lists. 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * This function may sleep and it has the same return values as 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         * blocking_notifier_chain_unregister(). 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
         */ 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        int ret; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        if ( 
        cpufreq_disabled()) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        return -EINVAL; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        switch (list) { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        case CPUFREQ_TRANSITION_NOTIFIER: 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        mutex_lock(&cpufreq_fast_switch_lock); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     ret = 
        srcu_notifier_chain_unregister( 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                                 &cpufreq_transition_notifier_list, nb); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        if (!ret && ! 
        WARN_ON(cpufreq_fast_switch_count >= 
        0)) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                   cpufreq_fast_switch_count++; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        mutex_unlock(&cpufreq_fast_switch_lock); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        break; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        case CPUFREQ_POLICY_NOTIFIER: 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     ret = 
        blocking_notifier_chain_unregister( 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                                                 &cpufreq_policy_notifier_list, nb); 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     
        break; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        default: 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                                     ret = -EINVAL; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       } 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

                       
        return ret; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         } 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        EXPORT_SYMBOL(cpufreq_unregister_notifier); 
       
 
      
    
   
    

    
     
   
    
   
    

去注册接口为注册接口的逆向操作，不再做过多解析。

3、使用样例

我们以loongson1-cpufreq.c作为样例

   
    

     
 
      
 
       
 
      
 
      
 
       
 
        static int ls1x_cpufreq_notifier(struct notifier_block *nb, 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        unsigned 
        long val, 
        void *data) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        if (val == CPUFREQ_POSTCHANGE) 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         current_cpu_data.udelay_val = loops_per_jiffy; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        return NOTIFY_OK; 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         } 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
       
 
      
     
 
      
 
       
 
      
 
      
 
       
 
        static 
        struct 
        notifier_block ls1x_cpufreq_notifier_block = { 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         .notifier_call = ls1x_cpufreq_notifier 
       
 
      
     
 
      
 
       
 
      
 
      
 
       

         }; 
       
 
      
    
   
    

该模块需要感知到频率的变化，需要在频率变化后来做一些事务处理，于是该模块就在回调中通过判断阶段为CPUFREQ_POSTCHANGE时做对应动作，并在初始化时通过调用cpufreq_register_notifier来注册。

4、软件处理

4.1 对cpufreq_transition_notifier_list的处理

现在该注册的模块已经注册进来了，那么cpufreq.c是如何回调注册的回调函数呢？cpufreq对cpufreq_transition_notifier_list链表的处理，统一封装到了函数cpufreq_notify_transition中来实现。

 实际代码以cppc_cpufreq.c为例：

 其中核心函数cpufreq_notify_transition的实现也是正常的逻辑实现，根据入参的不同分别处理

cpufreq_notify_transition函数会分别被cpufreq_freq_transition_begin和cpufreq_freq_transition_end来调用，而这2个函数则分别嵌入在了频率调换前和调换后调用，如此以来用户注册的回调会被最终调用到。

4.2 对cpufreq_policy_notifier_list的处理

对cpufreq_policy_notifier_list的调用，分别在cpufreq_policy_free和cpufreq_online中调用，分别针对policy移除和生效