Android中Linux suspend/resume流程

Android中Linux suspend/resume流程
首先我们从linux kernel 的suspend说起，不管你是使用echo mem > /sys/power/state 或者使用你的开发板已经拥有的power key 都可以实现系统进入suspend的功能，这是suspend的基础，即控制系统使suspend得到执行的机会，这里相信大家都可以理解，不再过多说明。

那么suspend得到了执行的机会又是怎么一步一步开始往下执行的呢？现在就开始我们的系统的电源管理之旅：

我们就通过echo mem > /sys/power/state这种方式来看，这样更容易被理解，位于/sys/power下面的这个state，做driver不知道那可说不过去，我们就看看这个state是在哪个地方创建的吧

kernel/kernel/power/suspend.c

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static int __init pm_init(void)
{
    int error = pm_start_workqueue();
    if (error)
        return error;
    hibernate_image_size_init();
    hibernate_reserved_size_init();
    power_kobj = kobject_create_and_add("power", NULL);
    if (!power_kobj)
        return -ENOMEM;
    return sysfs_create_group(power_kobj, &attr_group);
}

core_initcall(pm_init);

static int __init pm_init(void)
{
int error = pm_start_workqueue();
if (error)
return error;
hibernate_image_size_init();
hibernate_reserved_size_init();
power_kobj = kobject_create_and_add("power", NULL);
if (!power_kobj)
return -ENOMEM;
return sysfs_create_group(power_kobj, &attr_group);
}

core_initcall(pm_init);
这段代码很少却很重要，我关心的是他确实为我们在sys目录下先建了一个power目录，然后，return时创建了很多接口，其中一个就是state，以下是接口定义

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static struct attribute * g[] = {
    &state_attr.attr,
#ifdef CONFIG_PM_TRACE
    &pm_trace_attr.attr,
    &pm_trace_dev_match_attr.attr,
#endif
#ifdef CONFIG_PM_SLEEP
    &pm_async_attr.attr,
    &wakeup_count_attr.attr,
#ifdef CONFIG_PM_DEBUG
    &pm_test_attr.attr,
#endif
#ifdef CONFIG_USER_WAKELOCK
    &wake_lock_attr.attr,
    &wake_unlock_attr.attr,
#endif
#endif
    NULL,
};

static struct attribute_group attr_group = {
    .attrs = g,
};

static struct attribute * g[] = {
&state_attr.attr,
#ifdef CONFIG_PM_TRACE
&pm_trace_attr.attr,
&pm_trace_dev_match_attr.attr,
#endif
#ifdef CONFIG_PM_SLEEP
&pm_async_attr.attr,
&wakeup_count_attr.attr,
#ifdef CONFIG_PM_DEBUG
&pm_test_attr.attr,
#endif
#ifdef CONFIG_USER_WAKELOCK
&wake_lock_attr.attr,
&wake_unlock_attr.attr,
#endif
#endif
NULL,
};

static struct attribute_group attr_group = {
.attrs = g,
};上面你可以看到了这些接口了

我们在echo mem > /sys/power/state，或调用的我们的接口函数state_store，suspend也就才真正开始走出第一步

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static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
               const char *buf, size_t n)
{
#ifdef CONFIG_SUSPEND
#ifdef CONFIG_EARLYSUSPEND
    suspend_state_t state = PM_SUSPEND_ON;
#else
    suspend_state_t state = PM_SUSPEND_STANDBY;
#endif
    const char * const *s;
#endif
    char *p;
    int len;
    int error = -EINVAL;

    p = memchr(buf, '\n', n);
    len = p ? p - buf : n;

    /* First, check if we are requested to hibernate */
    if (len == 4 && !strncmp(buf, "disk", len)) {
        error = hibernate();
                goto Exit;
    }

#ifdef CONFIG_SUSPEND
    for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++) {
        if (*s && len == strlen(*s) && !strncmp(buf, *s, len))
            break;
    }
    if (state < PM_SUSPEND_MAX && *s)
#ifdef CONFIG_EARLYSUSPEND
        if (state == PM_SUSPEND_ON || valid_state(state)) {
            error = 0;
            request_suspend_state(state);
        }
#else
        error = enter_state(state);
#endif
#endif

Exit:
    return error ? error : n;
}

static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t n)
{
#ifdef CONFIG_SUSPEND
#ifdef CONFIG_EARLYSUSPEND
suspend_state_t state = PM_SUSPEND_ON;
#else
suspend_state_t state = PM_SUSPEND_STANDBY;
#endif
const char * const *s;
#endif
char *p;
int len;
int error = -EINVAL;

p = memchr(buf, '\n', n);
len = p ? p - buf : n;

/* First, check if we are requested to hibernate */
if (len == 4 && !strncmp(buf, "disk", len)) {
error = hibernate();
goto Exit;
}

#ifdef CONFIG_SUSPEND
for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++) {
  if (*s && len == strlen(*s) && !strncmp(buf, *s, len))
   break;
}
if (state < PM_SUSPEND_MAX && *s)
#ifdef CONFIG_EARLYSUSPEND
  if (state == PM_SUSPEND_ON || valid_state(state)) {
   error = 0;
   request_suspend_state(state);
  }
#else
  error = enter_state(state);
#endif
#endif

Exit:
return error ? error : n;
}这里我们echo mem > /sys/power/state，还有一种echo on > /sys/power/state，接着state_store进入reauest_suspend_state(state)，然后如果是on的话进入late_resume_work（在执行late_resume_work之前会向系统申请main_wake_lock），如果是mem进入early_suspend_work。

reauest_suspend_state函数路径：kernel/kernel/power/earlysuspend.c

补充：移动开发 , Android ,