一：runtime机构简介
何为runtime机制?也就是系统在非睡眠状态，设备在空暇时能够进入runtime suspend状态同一时候不依赖系统wake_lock机制。非空暇时运行runtime resume使得设备进入正常工作状态。
主要代码放在Runtime.c (drivers\base\power)中，同一时候附带的Runtime_pm.txt (documentation\power)有具体
说明。个參数usage_count与child_count同一时候为。
1：操作usage_count參数通常在HOST控制器驱动中，使用辅助runtime函数来完毕。
2：操作child_count通常由子设备来完毕父设备child_count的添加与降低。
child_count能够理解该设备活跃的子设备的个数。
通常由子设备睡后来让父设备进入休眠，依次递归进行。
二：以下重点分析一下rpm_suspend与rpm_resume
static int rpm_suspend(struct device *dev, int rpmflags)
__releases(&dev->power.lock) __acquires(&dev->power.lock)
{
int (*callback)(struct device *);
struct device *parent = NULL;
struct rpm_qos_data qos;
int retval;
trace_rpm_suspend(dev, rpmflags);
repeat:
retval = rpm_check_suspend_allowed(dev); //在这里检查usage_count与child_count。当非0存在时将使得该函数直接return。
if (retval < 0)
; /* Conditions are wrong. */
/* Synchronous suspends are not allowed in the RPM_RESUMING state. */
else if (dev->power.runtime_status == RPM_RESUMING &&
!(rpmflags & RPM_ASYNC))
retval = -EAGAIN;
if (retval)
goto out;
----------
/* Carry out an asynchronous or a synchronous suspend. */
if (rpmflags & RPM_ASYNC) { //异步情况，提交一个工作队列后退出
dev->power.request = (rpmflags & RPM_AUTO) ?
RPM_REQ_AUTOSUSPEND : RPM_REQ_SUSPEND;//当该suspend发起者支持auto suspend时rpmflags为RPM_REQ_AUTOSUSPEND，通常auto带有delay
time时延。
if (!dev->power.request_pending) {
dev->power.request_pending = true;
queue_work(pm_wq, &dev->power.work);
}
goto out;
}
--------------
/*
以下是选择回调函数。假设设备是挂在platform以下的，将运行pm_generic_runtime_suspend（）后运行device runtime suspend callback
这里的callback也就是我们在驱动里面注冊的idle,suspend,resume callback;
static const struct dev_pm_ops platform_dev_pm_ops = {
.runtime_suspend = pm_generic_runtime_suspend,
.runtime_resume = pm_generic_runtime_resume,
.runtime_idle = pm_generic_runtime_idle,
USE_PLATFORM_PM_SLEEP_OPS
};
int pm_generic_runtime_suspend(struct device *dev)
{
const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
int ret;
ret = pm && pm->runtime_suspend ? pm->runtime_suspend(dev) : 0;
return ret;
}
*/
if (dev->pm_domain)
callback = dev->pm_domain->ops.runtime_suspend;
else if (dev->type && dev->type->pm)
callback = dev->type->pm->runtime_suspend;
else if (dev->class && dev->class->pm)
callback = dev->class->pm->runtime_suspend;
else if (dev->bus && dev->bus->pm)
callback = dev->bus->pm->runtime_suspend;
else
callback = NULL;
if (!callback && dev->driver && dev->driver->pm)
callback = dev->driver->pm->runtime_suspend;
retval = rpm_callback(callback, dev);//运行回调函数。
if (retval)
goto fail;
no_callback:
__update_runtime_status(dev, RPM_SUSPENDED);
pm_runtime_deactivate_timer(dev);
if (dev->parent) {
parent = dev->parent;
atomic_add_unless(&parent->power.child_count, -1, 0);
}//假设该设备父设备存在，因为上面该设备已经运行到runtime suspend callback了，那么这时将父设备的子设备减一。
----------
/* Maybe the parent is now able to suspend. */
if (parent && !parent->power.ignore_children && !dev->power.irq_safe) {
spin_unlock(&dev->power.lock);
spin_lock(&parent->power.lock);
rpm_idle(parent, RPM_ASYNC);
spin_unlock(&parent->power.lock);
spin_lock(&dev->power.lock);
}//尝试让父设备进入idle。
-------------
}
static int rpm_resume(struct device *dev, int rpmflags)
__releases(&dev->power.lock) __acquires(&dev->power.lock)
{
int (*callback)(struct device *);
struct device *parent = NULL;
int retval = 0;
trace_rpm_resume(dev, rpmflags);
repeat:
if (dev->power.runtime_error)
retval = -EINVAL;
else if (dev->power.disable_depth > 0)//进行条件推断，disable_depth为禁止runtime，在pm_runtime_enable（）时会置为0；
retval = -EACCES;
if (retval)
goto out;
--------
if (dev->power.runtime_status == RPM_ACTIVE) {//当前状态为active时直接推出;
retval = 1;
goto out;
}
---------
/* Carry out an asynchronous or a synchronous resume. */
if (rpmflags & RPM_ASYNC) {
dev->power.request = RPM_REQ_RESUME;
if (!dev->power.request_pending) {
dev->power.request_pending = true;
queue_work(pm_wq, &dev->power.work);//异步情况，提交一个工作队列后退出
}
retval = 0;
goto out;
}
if (!parent && dev->parent) {
/*
* Increment the parent's usage counter and resume it if
* necessary. Not needed if dev is irq-safe; then the
* parent is permanently resumed.
*/
parent = dev->parent;
if (dev->power.irq_safe)
goto skip_parent;
spin_unlock(&dev->power.lock);
pm_runtime_get_noresume(parent);//在该设备resume前要先resume父设备。There Increment the parent's usage counter；
spin_lock(&parent->power.lock);
/*
* We can resume if the parent's runtime PM is disabled or it
* is set to ignore children.
*/
if (!parent->power.disable_depth
&& !parent->power.ignore_children) {
rpm_resume(parent, 0); //resume父设备
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;
}
skip_parent:
if (dev->power.no_callbacks)
goto no_callback; /* Assume success. */
dev->power.suspend_time = ktime_set(0, 0);
dev->power.max_time_suspended_ns = -1;
__update_runtime_status(dev, RPM_RESUMING);
/*选择同一时候运行设备resume callback*/
if (dev->pm_domain)
callback = dev->pm_domain->ops.runtime_resume;
else if (dev->type && dev->type->pm)
callback = dev->type->pm->runtime_resume;
else if (dev->class && dev->class->pm)
callback = dev->class->pm->runtime_resume;
else if (dev->bus && dev->bus->pm)
callback = dev->bus->pm->runtime_resume;
else
callback = NULL;
if (!callback && dev->driver && dev->driver->pm)
callback = dev->driver->pm->runtime_resume;
retval = rpm_callback(callback, dev);
if (retval) {
__update_runtime_status(dev, RPM_SUSPENDED);
pm_runtime_cancel_pending(dev);
} else {
no_callback:
__update_runtime_status(dev, RPM_ACTIVE);
if (parent)
atomic_inc(&parent->power.child_count);//该设备唤醒后添加父设备的子设备活跃数 child_count+1；
}
wake_up_all(&dev->power.wait_queue);
if (!retval)
rpm_idle(dev, RPM_ASYNC);
out:
if (parent && !dev->power.irq_safe) {
spin_unlock_irq(&dev->power.lock);
pm_runtime_put(parent); //减去刚才添加的the parent's usage counter;
spin_lock_irq(&dev->power.lock);
}
trace_rpm_return_int(dev, _THIS_IP_, retval);
return retval;
}
RPM机制整体来说就是管理总线结构和主次设备结构的电源,由于体系结构的因素，device套device的情况，最后就会形成一个device大树。runtime这套机制就能够从根到树顶都能管理得到。
通过上面分析我们知道当休眠时，先由子设备睡眠再让父设备休眠，递归进行，由下而上休眠。当唤醒时，是由上而下，递归唤醒。
三：实例分析
1：以msm_sdcc.c为例分析使用runtime辅助函数来实现device runtime功能：
在sdio数据读写完毕后会调用到msmsdcc_disable（）。之前会调用到msmsdcc_enable（）。
以此来实现runtime功能。
static int msmsdcc_disable(struct mmc_host *mmc)
{
---------
if (host->plat->disable_runtime_pm)
return -ENOTSUPP;
rc = pm_runtime_put_sync(mmc->parent); //使用runtime辅助函数。先将usage_count减一，再让设备进入idle
---------
}
static inline int pm_runtime_put_sync(struct device *dev)
{
return __pm_runtime_idle(dev, RPM_GET_PUT);
}
int pm_generic_runtime_idle(struct device *dev)
{
const struct dev_pm_ops *pm = dev->driver ?
dev->driver->pm : NULL;
if (pm && pm->runtime_idle) {
int ret = pm->runtime_idle(dev);//调用设备idle的callback
if (ret)
return ret;
}
pm_runtime_suspend(dev);//发起runtime suspend动作
return 0;
}
static int msmsdcc_enable(struct mmc_host *mmc)
{
--------
rc = pm_runtime_get_sync(dev);//使用runtime辅助函数，先将usage_count加一，再让设备进入resume
--------
}
static inline int pm_runtime_get_sync(struct device *dev)
{
return __pm_runtime_resume(dev, RPM_GET_PUT);
}
2：分析一段关于usb runtime的log：
<4>[ 22.281829] rpm_suspend name=usb1 usage_count=0 child_count=0 //device name为usb1 父设备名为msm_hsic_host,进入rpm_suspend
<4>[ 22.281860] rpm_suspend name=usb1 parent_name=msm_hsic_host p_usage_count=0 p_child_count=1 //在这里usb还没有进入suspend。故打印出的父设备的活跃子设备为1。
<4>[ 22.281890] rpm_suspend dev parent's child_count -1 //msm_hsic_host 的child_count -1；
<4>[ 22.281890] rpm_suspend name=usb1 usage_count=0 child_count=0
<4>[ 22.281921] rpm_suspend name=usb1 parent_name=msm_hsic_host p_usage_count=0 p_child_count=0 //msm_hsic_host 的child_count为0。
<4>[ 22.281951] rpm_suspend try dev parent going to sleep //让父设备进入休眠
<4>[ 22.281951] rpm_suspend name=usb1 usage_count=0 child_count=0
<4>[ 22.281982] rpm_suspend name=usb1 parent_name=msm_hsic_host p_usage_count=0 p_child_count=0
<4>[ 22.282135] rpm_suspend name=msm_hsic_host usage_count=0 child_count=0 //msm_hsic_host进入rpm_suspend，由上面发起
<4>[ 22.282165] rpm_suspend name=msm_hsic_host parent_name=platform p_usage_count=0 p_child_count=6 //msm_hsic_host的父设备还有6个活跃的子设备
<4>[ 22.282165] rpm_suspend dev parent's child_count -1 //msm_hsic_host已经休眠，让父设备的活跃的子设备减一；
<4>[ 22.282196] rpm_suspend name=msm_hsic_host usage_count=0 child_count=0
<4>[ 22.282226] rpm_suspend name=msm_hsic_host parent_name=platform p_usage_count=0 p_child_count=5
<4>[ 22.282226] rpm_suspend try dev parent going to sleep //试图让platform进入休眠
<4>[ 22.282257] rpm_suspend name=msm_hsic_host usage_count=0 child_count=0
<4>[ 22.282257] rpm_suspend name=msm_hsic_host parent_name=platform p_usage_count=0 p_child_count=5
<4>[ 22.635589] rpm_resume name=msm_hsic_host usage_count=1 child_count=0 //设备名为msm_hsic_host的进入rpm_resume,usage_count=1是由发起者添加的。
<4>[ 22.635620] rpm_resume name=msm_hsic_host parent_name=platform p_usage_count=0 p_child_count=5
<4>[ 22.635650] rpm_resume add parent usage count
<4>[ 22.635650] rpm_resume name=msm_hsic_host usage_count=1 child_count=0
<4>[ 22.635650] rpm_resume name=msm_hsic_host parent_name=platform p_usage_count=1 p_child_count=5
<4>[ 22.635772] rpm_resume name=msm_hsic_host usage_count=0 child_count=0
<4>[ 22.635772] rpm_resume name=msm_hsic_host parent_name=platform p_usage_count=1 p_child_count=5
<4>[ 22.635803] rpm_resume add parent child_count +1
<4>[ 22.635803] rpm_resume name=msm_hsic_host usage_count=0 child_count=0
<4>[ 22.635833] rpm_resume name=msm_hsic_host parent_name=platform p_usage_count=1 p_child_count=6
<4>[ 22.635833] rpm_resume over name=msm_hsic_host usage_count=0 child_count=0
<4>[ 22.635864] rpm_resume over name=msm_hsic_host parent_name=platform p_usage_count=0 p_child_count=6
<4>[ 22.635864] rpm_resume name=usb1 usage_count=1 child_count=0 //设备为usb1进入rpm_resume
<4>[ 22.635894] rpm_resume name=usb1 parent_name=msm_hsic_host p_usage_count=0 p_child_count=0
<4>[ 22.635894] rpm_resume add parent usage count
<4>[ 22.635894] rpm_resume name=usb1 usage_count=1 child_count=0
<4>[ 22.635925] rpm_resume name=usb1 parent_name=msm_hsic_host p_usage_count=1 p_child_count=0
<4>[ 22.671600] rpm_resume name=usb1 usage_count=1 child_count=0
<4>[ 22.671630] rpm_resume name=usb1 parent_name=msm_hsic_host p_usage_count=1 p_child_count=0
<4>[ 22.671630] rpm_resume add parent child_count +1
<4>[ 22.671661] rpm_resume name=usb1 usage_count=1 child_count=0
<4>[ 22.671661] rpm_resume name=usb1 parent_name=msm_hsic_host p_usage_count=1 p_child_count=1
<4>[ 22.671691] rpm_resume over name=usb1 usage_count=1 child_count=0
<4>[ 22.671691] rpm_resume over name=usb1 parent_name=msm_hsic_host p_usage_count=0 p_child_count=1
上面log充分说明了runtime_suspend是从子设备到父设备，递归休眠的。而runtime_resume则是相反的过程。
深入理解runtime pm机制。将会为调试设备不能进入runtime suspend打下坚实基础，通常linux中通讯总线都会採用runtime
电源管理机制，当I/O非busy时自己主动休眠，也就是通讯没有数据交互的时候的总线自己主动进入suspend。电源管理採用不用则停的方略，以此来降低功耗。
通常AP通过USB来外挂第三方MODEM,肯定会遇见休眠问题。因为usb通信速率能达到480Mbps，而sdio 100Mbps hs uart 4M,非常明显usb通信非常有优势，尤其在4G越来越普及的情况下。如今就是越来越来的AP+MODEM方案通过usb来通信的。
兴许有空再结合数据收发详尽分析usb休眠机制，Linux usb suspend机制。
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