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研发客服Run-time PM.
每个device或者bus都会向run-time PM core注册3个callback
struct dev_pm_ops {
...
int (*runtime_suspend)(struct device *dev);
int (*runtime_resume)(struct device *dev);
int (*runtime_idle)(struct device *dev);
...
};
每个device或者bus都会有2个计数器，一个是device的usage counter,一个是device的active状态的children个数。
当这个device的两个counter都减少为0的时候。
run-time PM core就会去调用runtime_idle函数，但是这里的idle函数可不是当前device的idle函数。
代码如下：
if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_idle) {
spin_unlock_irq(&dev->power.lock);
dev->bus->pm->runtime_idle(dev);
spin_lock_irq(&dev->power.lock);
} else if (dev->type && dev->type->pm && dev->type->pm->runtime_idle) {
spin_unlock_irq(&dev->power.lock);
dev->type->pm->runtime_idle(dev);
spin_lock_irq(&dev->power.lock);
} else if (dev->class && dev->class->pm
&& dev->class->pm->runtime_idle) {
spin_unlock_irq(&dev->power.lock);
dev->class->pm->runtime_idle(dev);
spin_lock_irq(&dev->power.lock);
}
按照dev->bus, dev->type, dev->class的顺序去调用。
大家会问了，那runtime_suspend函数什么时候调用？
runtime_suspend函数不会被RPM core主动去调用，一般情况下是在bus，或者class的idle函数里去调用。
例如：
static int xxx_runtime_idle(struct device *dev)
{
return pm_schedule_suspend(dev, 50);
}
pm_schedule_suspend函数会去调用device里的suspend函数，调用顺序代码如下：
if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_suspend) {
spin_unlock_irq(&dev->power.lock);
retval = dev->bus->pm->runtime_suspend(dev);
spin_lock_irq(&dev->power.lock);
dev->power.runtime_error = retval;
} else if (dev->type && dev->type->pm
&& dev->type->pm->runtime_suspend) {
spin_unlock_irq(&dev->power.lock);
retval = dev->type->pm->runtime_suspend(dev);
spin_lock_irq(&dev->power.lock);
dev->power.runtime_error = retval;
} else if (dev->class && dev->class->pm
&& dev->class->pm->runtime_suspend) {
spin_unlock_irq(&dev->power.lock);
retval = dev->class->pm->runtime_suspend(dev);
spin_lock_irq(&dev->power.lock);
dev->power.runtime_error = retval;
} else {
retval = -ENOSYS;
}
发现了吧，和idle顺序是一模一样哒。当然肯定也会有不一样了，否则runtime_suspend函数没存在意义了。在跑完此dev的bus or type or class的suspend函数以后。紧接着会做一个巨艰巨的任务，就是
if (parent && !parent->power.ignore_children) {
spin_unlock_irq(&dev->power.lock);
pm_request_idle(parent);
spin_lock_irq(&dev->power.lock);
}
会去调用当前这个device的parent device的idle函数！！！
之后会去递归的往上层调用。为啥会这么做呢？？？
其实RPM机制总体来说就是管理总线结构和主次设备结构的电源。
假如一个bus上有2个device。这个bus首先会有一个bus_type，其次还会有一个代表bus的device（谁说bus不是device了！）首先命名以下，bus device叫做Bdev, 两个bus上的子device是dev1, dev2。dev1,dev2是Bdev的子设备，也就是说dev1,dev2的parent是Bdev。
其中bus_type里会有一套runtime_pm的三个callback，Bdev自身还有另一套runtime_pm的三个callback。
当dev1的两个counter都为零了，就会调用bus_type里的runtime_idle，一般情况下这个idle会调用pm_runtime_suspend，仅按照上面的介绍，就会调用这个bus_type里的runtime_suspend call back。之后是不是就该是最重要的那一步了？pm_request_idle(parent);pm_request_idle里的一系列操作会首先判断parent的两个counter是否为零了，因为dev2还活着呢，所以条件不满足，返回！
当dev2也来这么一套之后，再调用pm_request_idle(parent);的时候，Bdev里的runtime_idle就能跑啦。
总结一下，bus_type的runtime_系列回调函数是用来处理bus上的device函数的。而bus自己的device的函数是用来处理自己的。
因为体系结构的因素，bus套bus的情况，最后就会形成一个device大树。runtime这套机制就可以从根到树顶都能管理得到。比如：I2C device挂在I2C bus上，I2C bus controller是PCI的一个设备，因为挂在PCI上。这个PCI bus一般还是在南桥上，然后再通过南桥在跑到北桥PCI上。。。。是不是块疯了。。。。但是有这么个递归电源管理。一切搞定。
说完了睡流程了。还有醒流程。
当device调用完suspend函数后，这个device就处于了一个suspended状态。当某个device被唤醒后，就会调用pm_runtime_get_sync类似的函数。这个函数做了啥捏？通过上述的睡过程，有点脑子的人就能想出醒流程，反着来呗！！！必须从大树顶往下跑，才能最后让根伸出来。代码如下：
if (!parent && dev->parent) {
/*
* Increment the parent's resume counter and resume it if
* necessary.
*/
parent = dev->parent;
spin_unlock(&dev->power.lock);
pm_runtime_get_noresume(parent);
spin_lock(&parent->power.lock);
/*
* We can resume if the parent's run-time PM is disabled or it
* is set to ignore children.
*/
if (!parent->power.disable_depth
&& !parent->power.ignore_children) {
__pm_runtime_resume(parent, false);
if (parent->power.runtime_status != RPM_ACTIVE)
retval = -EBUSY;
}
spin_unlock(&parent->power.lock);
spin_lock(&dev->power.lock);
if (retval)
goto out;
goto repeat;
}
首先跑这个device的parent的resume函数。之后
if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_resume) {
spin_unlock_irq(&dev->power.lock);
retval = dev->bus->pm->runtime_resume(dev);
spin_lock_irq(&dev->power.lock);
dev->power.runtime_error = retval;
} else if (dev->type && dev->type->pm
&& dev->type->pm->runtime_resume) {
spin_unlock_irq(&dev->power.lock);
retval = dev->type->pm->runtime_resume(dev);
spin_lock_irq(&dev->power.lock);
dev->power.runtime_error = retval;
} else if (dev->class && dev->class->pm
&& dev->class->pm->runtime_resume) {
spin_unlock_irq(&dev->power.lock);
retval = dev->class->pm->runtime_resume(dev);
spin_lock_irq(&dev->power.lock);
dev->power.runtime_error = retval;
} else {
retval = -ENOSYS;
}
跑的是bus的resume函数。通过这个函数进行递归，直到递归到树顶后,树顶的resume就开始run了，run完一个往下面继续传，直到我们的这一连串device的resume函数都跑完，我们的device就算醒了。
RPM常用接口如下：
void pm_runtime_init(struct device *dev);
- initialize the device run-time PM fields in 'struct dev_pm_info'
void pm_runtime_remove(struct device *dev);
- make sure that the run-time PM of the device will be disabled after
removing the device from device hierarchy
int pm_runtime_idle(struct device *dev);
- execute the subsystem-level idle callback for the device; returns 0 on
success or error code on failure, where -EINPROGRESS means that
->runtime_idle() is already being executed
int pm_runtime_suspend(struct device *dev);
- execute the subsystem-level suspend callback for the device; returns 0 on
success, 1 if the device's run-time PM status was already 'suspended', or
error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt
to suspend the device again in future
int pm_runtime_resume(struct device *dev);
- execute the subsystem-level resume callback for the device; returns 0 on
success, 1 if the device's run-time PM status was already 'active' or
error code on failure, where -EAGAIN means it may be safe to attempt to
resume the device again in future, but 'power.runtime_error' should be
checked additionally
int pm_request_idle(struct device *dev);
- submit a request to execute the subsystem-level idle callback for the
device (the request is represented by a work item in pm_wq); returns 0 on
success or error code if the request has not been queued up
int pm_schedule_suspend(struct device *dev, unsigned int delay);
- schedule the execution of the subsystem-level suspend callback for the
device in future, where 'delay' is the time to wait before queuing up a
suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work
item is queued up immediately); returns 0 on success, 1 if the device's PM
run-time status was already 'suspended', or error code if the request
hasn't been scheduled (or queued up if 'delay' is 0); if the execution of
->runtime_suspend() is already scheduled and not yet expired, the new
value of 'delay' will be used as the time to wait
int pm_request_resume(struct device *dev);
- submit a request to execute the subsystem-level resume callback for the
device (the request is represented by a work item in pm_wq); returns 0 on
success, 1 if the device's run-time PM status was already 'active', or
error code if the request hasn't been queued up
void pm_runtime_get_noresume(struct device *dev);
- increment the device's usage counter
int pm_runtime_get(struct device *dev);
- increment the device's usage counter, run pm_request_resume(dev) and
return its result
int pm_runtime_get_sync(struct device *dev);
- increment the device's usage counter, run pm_runtime_resume(dev) and
return its result
void pm_runtime_put_noidle(struct device *dev);
- decrement the device's usage counter
int pm_runtime_put(struct device *dev);
- decrement the device's usage counter, run pm_request_idle(dev) and return
its result
int pm_runtime_put_sync(struct device *dev);
- decrement the device's usage counter, run pm_runtime_idle(dev) and return
its result
void pm_runtime_enable(struct device *dev);
- enable the run-time PM helper functions to run the device bus type's
run-time PM callbacks described in Section 2
int pm_runtime_disable(struct device *dev);