電子發(fā)燒友App
1.??????用戶空間的接口
在kernel/power/main.c中，定義了一組sysfs的屬性文件，其中一個(gè)定義是：
power_attr(state);
把這個(gè)宏展開(kāi)后:
[cpp]?view plain?copy
staticstruct?kobj_attribute?state_attr?=?{?\??
.attr?={????????????????????????????????\??
.name?=?"state",????\??
.mode?=?0644,???????????????????????????\??
},????????????????????????????????????????????\??
.show??????=state_show,???????????????????????????\??
.store???????=state_store,??????????????????\??
}??
我們?cè)倏纯磎ain.c的入口：
[cpp]?view plain?copy
staticint?__init?pm_init(void)??
{??
......??
power_kobj?=kobject_create_and_add("power",?NULL);??
if?(!power_kobj)??
return?-ENOMEM;??
return?sysfs_create_group(power_kobj,&attr_group);??
}??
?
顯然，該函數(shù)執(zhí)行后，會(huì)在生成/sys/power目錄，該目錄下會(huì)建立一系列屬性文件，其中一個(gè)就是/sys/power/state文件。用戶空間向該文件的寫(xiě)入將會(huì)導(dǎo)致state_store被調(diào)用，讀取該文件將會(huì)導(dǎo)致state_show函數(shù)被調(diào)用。
現(xiàn)在回到Android的HAL層中，查看一下代碼：hardware/libhardware_legacy/power/power.c：
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//定義寫(xiě)入/sys/power/state的命令字符串??
staticconst?char?*off_state?=?"mem";??
staticconst?char?*on_state?=?"on";??
//打開(kāi)/sys/power/state等屬性文件，保存相應(yīng)的文件描述符??
staticint??
open_file_descriptors(constchar?*?const?paths[])??
{??
int?i;??
for?(i=0;?i
int?fd?=?open(paths[i],?O_RDWR);??
if?(fd?
fprintf(stderr,?"fatal?erroropening?"%s"\n",?paths[i]);??
g_error?=?errno;??
return?-1;??
}??
g_fds[i]?=?fd;??
}??
g_error?=?0;??
return?0;??
}??
最終，用戶空間的電源管理系統(tǒng)會(huì)調(diào)用set_screen_state函數(shù)來(lái)觸發(fā)suspend的流程，該函數(shù)實(shí)際上就是往/sys/power/state文件寫(xiě)入"mem"或"on"命令字符串。
[cpp]?view plain?copy
int??
set_screen_state(inton)??
{??
......??
initialize_fds();??
......??
char?buf[32];??
int?len;??
if(on)??
len?=?snprintf(buf,?sizeof(buf),"%s",?on_state);??
else??
len?=?snprintf(buf,?sizeof(buf),"%s",?off_state);??
buf[sizeof(buf)?-?1]?=?'\0';??
len?=?write(g_fds[REQUEST_STATE],?buf,len);??
......??
return?0;??
}??
/********************************************************************************************/
聲明：本博內(nèi)容均由http://blog.csdn.net/droidphone原創(chuàng)，轉(zhuǎn)載請(qǐng)注明出處，謝謝！
/********************************************************************************************/
2.??????內(nèi)核中數(shù)據(jù)結(jié)構(gòu)和接口
與earlysuspend相關(guān)的數(shù)據(jù)結(jié)構(gòu)和接口都在earlysuspend.h中進(jìn)行了定義。
- early_suspend 結(jié)構(gòu)
[cpp]?view plain?copy
struct?early_suspend?{??
#ifdef?CONFIG_HAS_EARLYSUSPEND??
structlist_head?link;??
int?level;??
void(*suspend)(struct?early_suspend?*h);??
void(*resume)(struct?early_suspend?*h);??
#endif??
};??
希望執(zhí)行early suspend的設(shè)備，他的設(shè)備驅(qū)動(dòng)程序需要向電源管理系統(tǒng)注冊(cè)，該結(jié)構(gòu)體用于向電源管理系統(tǒng)注冊(cè)earlysuspend/lateresume，當(dāng)電源管理系統(tǒng)啟動(dòng)suspend流程時(shí)，回調(diào)函數(shù)suspend會(huì)被調(diào)用，相反，resume的最后階段，回調(diào)函數(shù)resume會(huì)被調(diào)用，level字段用于調(diào)整該結(jié)構(gòu)體在注冊(cè)鏈表中的位置，suspend時(shí)，level的數(shù)值越小，回調(diào)函數(shù)的被調(diào)用的時(shí)間越早，resume時(shí)則反過(guò)來(lái)。Android預(yù)先定義了3個(gè)level等級(jí)：
[cpp]?view plain?copy
enum?{??
EARLY_SUSPEND_LEVEL_BLANK_SCREEN?=?50,??
EARLY_SUSPEND_LEVEL_STOP_DRAWING?=?100,??
EARLY_SUSPEND_LEVEL_DISABLE_FB?=?150,??
};??
[cpp]?view plain?copy
如果你想你的設(shè)備在FB設(shè)備被禁止之前執(zhí)行他的early?suspend回調(diào)，設(shè)備驅(qū)動(dòng)程序應(yīng)該把level值設(shè)定為小于150的某個(gè)數(shù)值，然后向系統(tǒng)注冊(cè)early_suspend結(jié)構(gòu)。注冊(cè)和反注冊(cè)函數(shù)是：??
void register_early_suspend(struct early_suspend *handler);
void unregister_early_suspend(struct early_suspend *handler);
- early_suspend_handlers鏈表
所有注冊(cè)到系統(tǒng)中的early_suspend結(jié)構(gòu)都會(huì)按level值按順序加入到全局鏈表early_suspend_handlers中。
3.??????工作流程
首先，我們從kernel/power/wakelock.c中的初始化函數(shù)開(kāi)始：
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static?int?__init?wakelocks_init(void)??
{??
int?ret;??
int?i;??
......??
for?(i?=?0;?i?
INIT_LIST_HEAD(&active_wake_locks[i]);??
......??
wake_lock_init(&main_wake_lock,?WAKE_LOCK_SUSPEND,?"main");??
wake_lock(&main_wake_lock);??
wake_lock_init(&unknown_wakeup,?WAKE_LOCK_SUSPEND,?"unknown_wakeups");??
......??
ret?=?platform_device_register(&power_device);??
ret?=?platform_driver_register(&power_driver);??
......??
suspend_work_queue?=?create_singlethread_workqueue("suspend");??
......??
return?0;??
}??
可以看到，顯示初始化active_wake_locks鏈表數(shù)組，然后初始化并且鎖住main_wake_lock，注冊(cè)平臺(tái)設(shè)備power_device，這些數(shù)組、鎖和power_device我們?cè)诤罄m(xù)文章再討論，這里我們關(guān)注的最后一個(gè)動(dòng)作：創(chuàng)建了一個(gè)工作隊(duì)列線程suspend_work_queue，該工作隊(duì)列是earlysuspend的核心所在。
系統(tǒng)啟動(dòng)完成后，相關(guān)的驅(qū)動(dòng)程序通過(guò)register_early_suspend()函數(shù)注冊(cè)了early suspend特性，等待一段時(shí)間后，如果沒(méi)有用戶活動(dòng)（例如按鍵、觸控等操作），用戶空間的電源管理服務(wù)最終會(huì)調(diào)用第一節(jié)提到的set_screen_state()函數(shù)，透過(guò)sysfs，進(jìn)而會(huì)調(diào)用到內(nèi)核中的state_store()：
[cpp]?view plain?copy
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?
if?(*s?&&?len?==?strlen(*s)?&&?!strncmp(buf,?*s,?len))??
break;??
}??
if?(state?
#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;??
}??
看到了沒(méi)，前一篇文章說(shuō)過(guò)，suspend to disk做了特殊處理，這里直接比較傳入的字符串，而不是使用后續(xù)的pm_states數(shù)組，這里我不關(guān)心suspend to disk，所以略過(guò)hibernate的分析。
緊接著，通過(guò)pm_states數(shù)組，根據(jù)命令字符串查詢得到請(qǐng)求的狀態(tài)，默認(rèn)情況下，Android的內(nèi)核都會(huì)配置了CONFIG_EARLYSUSPEND，所以會(huì)調(diào)用request_suspend_state()函數(shù)，不過(guò)在調(diào)用該函數(shù)之前會(huì)先valid_state()一下，這給了平臺(tái)相關(guān)的代碼一個(gè)機(jī)會(huì)確認(rèn)該平臺(tái)是否支持所請(qǐng)求的電源狀態(tài)。valid_state()的具體實(shí)現(xiàn)請(qǐng)參考內(nèi)核代碼樹(shù)。
[cpp]?view plain?copy
void?request_suspend_state(suspend_state_t?new_state)??
{??
unsigned?long?irqflags;??
int?old_sleep;??
spin_lock_irqsave(&state_lock,?irqflags);??
old_sleep?=?state?&?SUSPEND_REQUESTED;??
......??
if?(!old_sleep?&&?new_state?!=?PM_SUSPEND_ON)?{??
state?|=?SUSPEND_REQUESTED;??
if?(queue_work(suspend_work_queue,?&early_suspend_work))??
pr_info("early_suspend_work?is?in?queue?already\n");??
}?else?if?(old_sleep?&&?new_state?==?PM_SUSPEND_ON)?{??
state?&=?~SUSPEND_REQUESTED;??
wake_lock(&main_wake_lock);??
if?(!queue_work(suspend_work_queue,&late_resume_work))??
pr_info("late_resume_work?is?in?queue?already\n");??
}??
requested_suspend_state?=?new_state;??
spin_unlock_irqrestore(&state_lock,?irqflags);??
}??
還記得前面初始化時(shí)建立的工作隊(duì)列suspend_woek_queue嗎？根據(jù)之前的電源狀態(tài)和請(qǐng)求的狀態(tài)， request_suspend_state()只是簡(jiǎn)單地向suspend_work_queue中加入early_suspend_work或者是late_resume_work并調(diào)度他們執(zhí)行。early_suspend_work的工作函數(shù)是early_suspend()：
staticvoid early_suspend(struct work_struct *work)
{
struct early_suspend *pos;
unsigned long irqflags;
int abort = 0;
mutex_lock(&early_suspend_lock);
spin_lock_irqsave(&state_lock,irqflags);
if (state == SUSPEND_REQUESTED)
state |= SUSPENDED;
else
abort = 1;
spin_unlock_irqrestore(&state_lock,irqflags);
if (abort) {
......
}
......
list_for_each_entry(pos,&early_suspend_handlers, link) {
if (pos->suspend != NULL) {
if (debug_mask &DEBUG_SUSPEND)
printk(KERN_DEBUG"pos->suspend: %pF begin\n", pos->suspend);
pos->suspend(pos);
if (debug_mask &DEBUG_SUSPEND)
printk(KERN_DEBUG"pos->suspend: %pF finish\n", pos->suspend);
}
}
mutex_unlock(&early_suspend_lock);
if (debug_mask & DEBUG_SUSPEND)
pr_info("early_suspend:sync\n");
sys_sync();
abort:
spin_lock_irqsave(&state_lock,irqflags);
if (state ==SUSPEND_REQUESTED_AND_SUSPENDED)
wake_unlock(&main_wake_lock);
spin_unlock_irqrestore(&state_lock,irqflags);
}
終于看到啦，early_suspend()遍歷early_suspend_handlers鏈表，從中取出各個(gè)驅(qū)動(dòng)程序注冊(cè)的early_suspend結(jié)構(gòu)，然后調(diào)用它的suspend回調(diào)函數(shù)。最后，釋放main_wake_lock鎖，至此整個(gè)earlysuspend的流程完成。下面的序列圖清晰地表明了整個(gè)調(diào)用的過(guò)程：
圖3.1? early suspend調(diào)用流程
但是，這時(shí)整個(gè)系統(tǒng)只是處于所謂的idle狀態(tài)，cpu還在工作，后臺(tái)進(jìn)程也在工作中，那什么時(shí)候系統(tǒng)會(huì)真正地進(jìn)入睡眠狀態(tài)？注意到最后一句關(guān)鍵的調(diào)用了沒(méi)有：
wake_unlock(&main_wake_lock);
?
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