UFS Power Management 介绍

一 . UFS Power Management Overview

1. UFS Power Management 管理UFS Power相关资源，

在收到访问请求的时候唤醒UFS工作，切换为工作模式，在完成请求后让UFS进行睡眠，切换为睡眠模式，能够节省功耗，提高续航。

主要是分为UFS Runtime Power Management和UFS System Power Management。

2. UFS Runtime Power Management:

UFS模块运行时睡眠唤醒机制，只需要UFS模块空闲，即可进入睡眠状态，不受其他模块的睡眠唤醒状态影响，通俗点讲就是个人自扫门前雪。

3. UFS System Power Management:

UFS系统睡眠唤醒机制，和系统的睡眠唤醒状态有关，需要系统所有的模块都睡眠下去，UFS 模块才会睡眠下去，当只有存在系统一个模块是唤醒状态/或者系统存在唤醒源导致睡眠部下去，UFS模块也是不能成功睡眠下去，通俗点讲就是有福同享，有难同当，不放弃任何一个民众。

二 . UFS Power Management Detail

1. UFS Runtime Power Management :

(1) UFS Runtime Power Management是在Linux Kernel RPM Framework下进行管理的，在没有访问请求/UFS空闲的时候，将UFS置为睡眠状态，当UFS有访问请求/不是空闲状态时，将UFS置为唤醒状态。

(2) UFS Driver RPM Power Management 主要是管理UFS Device Power Mode State和MPHY Link State。

UFS PM Level State划分为六个等级，默认rpm_lvl 是3，也就是UFS_SLEEP_PWR_MODE, UIC_LINK_ACTIVE_STATE。

UFS_SLEEP_PWR_MODE：指的是UFS Device PowerMode为Sleep Mode, 需要发送SSU命令切换UFS Power Mode。

UIC_LINK_ACTIVE_STATE：指的是将UFS MPHY Link设置为Hibernate状态，需要发送DME_HIBERNATE_ENTER命令切换Link Status.

struct ufs_pm_lvl_states ufs_pm_lvl_states[] = {{UFS_ACTIVE_PWR_MODE, UIC_LINK_ACTIVE_STATE},{UFS_ACTIVE_PWR_MODE, UIC_LINK_HIBERN8_STATE},{UFS_SLEEP_PWR_MODE, UIC_LINK_ACTIVE_STATE},{UFS_SLEEP_PWR_MODE, UIC_LINK_HIBERN8_STATE},{UFS_POWERDOWN_PWR_MODE, UIC_LINK_HIBERN8_STATE},{UFS_POWERDOWN_PWR_MODE, UIC_LINK_OFF_STATE},
};

(3) UFS RPM 相关Sysfs节点：


UFS RPM Sysfs节点目录： /sys/device/platform/soc/1d84.ufshci/powerUFS RPM 相关节点：1. control： Report/change current runtime PM setting of the device
**  Runtime power management of a device can be blocked with the help of*   this attribute.  All devices have one of the following two values for*  the power/control file:*     + "auto\n" to allow the device to be power managed at run time;*     + "on\n" to prevent the device from being power managed at run time;2. autosuspend_delay_ms - Report/change a device's autosuspend_delay value**   Some drivers don't want to carry out a runtime suspend as soon as a*   device becomes idle; they want it always to remain idle for some period*    of time before suspending it.  This period is the autosuspend_delay*    value (expressed in milliseconds) and it can be controlled by the user.*    If the value is negative then the device will never be runtime* suspended.3. runtime_active_time: report runtime active status totol time.4. runtime_suspended_time: report runtime suspended status totol time.5. runtime_status: report runtime status.

(4) UFS 设备Runtime Power Management状态：


/** Device run-time power management status.** These status labels are used internally by the PM core to indicate the* current status of a device with respect to the PM core operations.  They do* not reflect the actual power state of the device or its status as seen by the* driver.** RPM_ACTIVE     Device is fully operational.  Indicates that the device*            bus type's ->runtime_resume() callback has completed*           successfully.** RPM_SUSPENDED   Device bus type's ->runtime_suspend() callback has*         completed successfully.  The device is regarded as*         suspended.** RPM_RESUMING       Device bus type's ->runtime_resume() callback is being*         executed.** RPM_SUSPENDING  Device bus type's ->runtime_suspend() callback is being*            executed.*/enum rpm_status {RPM_ACTIVE = 0,RPM_RESUMING,RPM_SUSPENDED,RPM_SUSPENDING,
};

(5) UFS 驱动常用Runtime PM使用接口和使用场景

在访问UFS 设备之前，为了防止UFS 进入Suspend , 我们需要调用以下两个接口增加设备使用计数，然后唤醒UFS 设备(Resume)为Active状态，这里UFS设备指的是UFS Host Controller,

Note：不管是UFS驱动还是USB驱动还是其他驱动，在访问设备之前都应该遵循以上流程，唤醒设备为Active状态，保证设备正常工作，否则如果设备进入了Suspend状态去访问会出现未知的错误。

pm_runtime_get_sync

pm_runtime_get

访问UFS设备之后，就可以让UFS 设备进入Suspend, 我们需要调用以下两个接口减少设备使用技术，然后使得UFS设备进入睡眠状态(Suspended), 这里UFS设备指的是UFS Host Controller.

pm_runtime_put

pm_runtime_put_sync

下面是一个具体的使用场景：

在对UFS Host Controller做访问之前，调用pm,_runtime_get_sync增加设备引用计数，唤醒设备，然后对设备进行访问操作，访问完成后调用pm_runtimr_put_sync减少设备引用计数，让设备睡眠。

int ufshcd_clk_scaling_enable(struct ufs_hba *hba, int value)
{int err;value = !!value;mutex_lock(&ufshcd_clkscale_lock);if (value == hba->clk_scaling.is_allowed)goto out;// 获取UFS PM Runtime 资源，增加PM Usage Count, 让UFS Host处于Active Statuspm_runtime_get_sync(hba->dev);  ufshcd_hold(hba, false);cancel_work_sync(&hba->clk_scaling.suspend_work);cancel_work_sync(&hba->clk_scaling.resume_work);hba->clk_scaling.is_allowed = value;if (value) {ufshcd_resume_clkscaling(hba);} else {ufshcd_suspend_clkscaling(hba);err = ufshcd_devfreq_scale(hba, true);if (err)dev_err(hba->dev, "%s: failed to scale clocks up %d\n",__func__, err);}ufshcd_release(hba, false);// 释放UFS PM Runtime资源，减少PM Usage Count, 让UFS Host处于Suspend Statuspm_runtime_put_sync(hba->dev);
out:mutex_unlock(&ufshcd_clkscale_lock);return 0;
}

阻塞UFS设备在Linux RPM Power Management 管理运行时进入Suspend.

增加设备引用计数和清除设备power.runtime_auto标志

除非调用pm_runtime_allow，否则UFS设备不会在运行的时候进入Suspend状态

pm_runtime_forbid

UFS设备在Linux RPM Power Management 管理运行时允许挂起(进入Suspended)

减少设备引用计数和设置设备power.runtime_auto标志

pm_runtime_allow

下面是一个具体的使用场景：

static const char ctrl_auto[] = "auto";
static const char ctrl_on[] = "on";

static ssize_t control_show(struct device *dev, struct device_attribute *attr,
           char *buf)
{
   return sprintf(buf, "%s\n",
               dev->power.runtime_auto ? ctrl_auto : ctrl_on);
}

static ssize_t control_store(struct device * dev, struct device_attribute *attr,
           const char * buf, size_t n)
{
   device_lock(dev);
   if (sysfs_streq(buf, ctrl_auto))
       pm_runtime_allow(dev);
   else if (sysfs_streq(buf, ctrl_on))
       pm_runtime_forbid(dev);
   else
       n = -EINVAL;
   device_unlock(dev);
   return n;
}

2. UFS System Power Management:

(1)UFS System Power Management是受整个内核系统影响的，需要内核系统所有模块都睡眠了或者内核系统没有唤醒事件，UFS设备才会进入UFS System Suspend。

UFS手机功耗续航测试就是在整个系统进入System Suspend(包括UFS System Suspend)后进行测试的，相关开发同事需要对整个系统的System Suspend/Resume 机制非常了解，才能清晰的定位到某个模块影响了系统进入System Suspend,导致功耗问题。

（2） UFS Driver RPM Power Management 主要是管理UFS Device Power Mode State和 MPHY Link State 还有UFS Device的供电VCC。

UFS PM Level State划分为六个等级，默认spm_lvl 是3，也就是UFS_SLEEP_PWR_MODE, UIC_LINK_ACTIVE_STATE。

UFS_SLEEP_PWR_MODE：指的是UFS Device PowerMode为Sleep Mode, 需要发送SSU命令切换UFS Power Mode。

UIC_LINK_ACTIVE_STATE：指的是将UFS MPHY Link设置为Hibernate状态，需要发送 DME_HIBERNATE_ENTER命令切换Link Status.

VCC： UFS Device进入System Suspend的时候，会将VCC电压关闭节省耗电，减少功耗。

(3) UFS System Suspend相关Sysfs节点：

系统PM节点目录： /sys/power/*

wake_lock：系统唤醒锁，如果有进程持有wake_lock, 整个系统就不会进入System Suspend, 当然UFS 设备也不能进入system suspend.

wake_unlock: 释放系统唤醒锁，让整个系统可以进入System Suspend, 当然UFS 设备也能进入system suspend.

(4) UFS 设备相关System PM状态：

系统System PM 相关状态：

#define PM_SUSPEND_ON       ((__force suspend_state_t) 0)
#define PM_SUSPEND_TO_IDLE   ((__force suspend_state_t) 1)
#define PM_SUSPEND_STANDBY   ((__force suspend_state_t) 2)
#define PM_SUSPEND_MEM       ((__force suspend_state_t) 3)
#define PM_SUSPEND_MIN       PM_SUSPEND_TO_IDLE
#define PM_SUSPEND_MAX       ((__force suspend_state_t) 4)

kernel/power/main.c

static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
           const char *buf, size_t n)
{
   suspend_state_t state;
   int error;

error = pm_autosleep_lock();
   if (error)
       return error;

if (pm_autosleep_state() > PM_SUSPEND_ON) {
       error = -EBUSY;
       goto out;
   }

state = decode_state(buf, n);
   if (state < PM_SUSPEND_MAX) {
       if (state == PM_SUSPEND_MEM)
           state = mem_sleep_current;

error = pm_suspend(state);
   } else if (state == PM_SUSPEND_MAX) {
       error = hibernate();
   } else {
       error = -EINVAL;
   }

out:
   pm_autosleep_unlock();
   return error ? error : n;
}

UFS System PM相关状态：

/* Used to differentiate the power management options */
enum ufs_pm_op {
   UFS_RUNTIME_PM,
   UFS_SYSTEM_PM,
   UFS_SHUTDOWN_PM,
};

/**
* ufshcd_system_suspend - system suspend routine
* @hba: per adapter instance
*
* Check the description of ufshcd_suspend() function for more details.
*
* Returns 0 for success and non-zero for failure
*/
int ufshcd_system_suspend(struct ufs_hba *hba)
{
   int ret = 0;
   ktime_t start = ktime_get();

if (!hba || !hba->is_powered)
       return 0;

if ((ufs_get_pm_lvl_to_dev_pwr_mode(hba->spm_lvl) ==
   hba->curr_dev_pwr_mode) &&
   (ufs_get_pm_lvl_to_link_pwr_state(hba->spm_lvl) ==
   hba->uic_link_state))
       goto out;

if (pm_runtime_suspended(hba->dev)) {
       /*
       * UFS device and/or UFS link low power states during runtime
       * suspend seems to be different than what is expected during
       * system suspend. Hence runtime resume the devic & link and
       * let the system suspend low power states to take effect.
       * TODO: If resume takes longer time, we might have optimize
       * it in future by not resuming everything if possible.
       */
       ret = ufshcd_runtime_resume(hba);
       if (ret)
           goto out;
   }

ret = ufshcd_suspend(hba, UFS_SYSTEM_PM);
out:
   trace_ufshcd_system_suspend(dev_name(hba->dev), ret,
       ktime_to_us(ktime_sub(ktime_get(), start)),
       hba->curr_dev_pwr_mode, hba->uic_link_state);
   if (!ret)
       hba->is_sys_suspended = true;
   return ret;
}
EXPORT_SYMBOL(ufshcd_system_suspend);

（6）UFS 驱动常用System PM使用接口和使用场景：

系统开始进入System Suspend的时候，会循环遍历每个设备都进入System Suspend状态，包括UFS设备，UFS驱动没有显性调用System PM的接口，主要是受系统Suspend机制管理，当系统开始进入Suspend流程的时候，UFS设备也是空闲的状态的时候，此时UFS设备就会进入System Suspend的状态，UFS驱动发送SSU命令让UFS Device进入SLEEP Mode, 发送DME_HIBER_ENTER让MPHY Link 进入Hibernate状态，并且UFS Device的VCC供电也会关闭，节省功耗。

三. 参考资料

1. Kernel System Power Management Source Code

2 . Kernel Runtime Power Management Source Code

3. Kernel UFS Power Management Source Code