arm电源管理(1)——apm.c.doc

arm电源管理(1)-apm.c - 内核版本比较旧了由于arm系统中没有bios设备, 所以只能为arm系统创建一个虚拟的字符设备与用户空间进行通讯. 这就是/arch/arm/kernel/amp.c1. 工作原理: 这个apm中实现一个misc设备,实质上也是一个字符设备, misc设备的主设备号是10, 而apm_bios作为一个misc设备, 次设备号是134. 定义为:/* The apm_bios device is one of the misc char devices.* This is its minor number.*/#define APM_MINOR_DEV 134 这个apm_bios设备通过ioctl系统调用和用户空间进行通讯, 即当用户进程通过ioctl发来suspend命令时, 它就传给内核, 使系统进入suspend状态. 2. 初始化static int _init apm_init(void) int ret; if (apm_disabled) printk(KERN_NOTICE apm: disabled on user request.n); return -ENODEV; if (PM_IS_ACTIVE() printk(KERN_NOTICE apm: overridden by ACPI.n); return -EINVAL; pm_active = 1; /创建一个线程, 用于处理事件队列, 工作函数是kapmd /这个线程好像在arm中没有作用? ret = kernel_thread(kapmd, NULL, CLONE_KERNEL); if (ret suser = capable(CAP_SYS_ADMIN); as-writer = (filp-f_mode & FMODE_WRITE) = FMODE_WRITE; as-reader = (filp-f_mode & FMODE_READ) = FMODE_READ; /将这个用户加入用户队列 down_write(&user_list_lock); list_add(&as-list, &apm_user_list); up_write(&user_list_lock); /这是一个传递私有数据的一个通用方式 filp-private_data = as; return as ? 0 : -ENOMEM;当用户空间进程去读这个设备时, 这个函数就会被调用. 这个函数的主要作用是将事件读出到用户空间static ssize_t apm_read(struct file *fp, char _user *buf, size_t count, loff_t *ppos) struct apm_user *as = fp-private_data; apm_event_t event; int i = count, ret = 0; if (count queue) & fp-f_flags & O_NONBLOCK) return -EAGAIN; /否则等待到队列非空为止, wait_event_interruptible(apm_waitqueue, !queue_empty(&as-queue); /将队列中的事件复制给用户空间 while (i = sizeof(event) & !queue_empty(&as-queue) event = queue_get_event(&as-queue); ret = -EFAULT; if (copy_to_user(buf, &event, sizeof(event) break; /设置状态 if (event = APM_SYS_SUSPEND | event = APM_USER_SUSPEND) as-suspend_state = SUSPEND_READ; buf += sizeof(event); i -= sizeof(event); if (i private_data; poll_wait(fp, &apm_waitqueue, wait); return queue_empty(&as-queue) ? 0 : POLLIN | POLLRDNORM;/这个是这个设备的核心函数, 用于内核与用户空间交互/* apm_ioctl - handle APM ioctl* APM_IOC_SUSPEND* This IOCTL is overloaded, and performs two functions. It is used to:* - initiate a suspend* - acknowledge a suspend read from /dev/apm_bios.* Only when everyone who has opened /dev/apm_bios with write permission* has acknowledge does the actual suspend happen.*/static intapm_ioctl(struct inode * inode, struct file *filp, u_int cmd, u_long arg) struct apm_user *as = filp-private_data; unsigned long flags; int err = -EINVAL; if (!as-suser | !as-writer) return -EPERM; switch (cmd) case APM_IOC_SUSPEND: as-suspend_result = -EINTR; if (as-suspend_state = SUSPEND_READ) /* * If we read a suspend command from /dev/apm_bios, * then the corresponding APM_IOC_SUSPEND ioctl is * interpreted as an acknowledge. */ as-suspend_state = SUSPEND_ACKED; suspends_pending-; else /* * Otherwise it is a request to suspend the system. * Queue an event for all readers, and expect an * acknowledge from all writers who havent already * acknowledged. */ queue_event(APM_USER_SUSPEND, as); /* * If there are no further acknowledges required, suspend * the system. */ if (suspends_pending = 0) apm_suspend(); /系统进入suspend状态 /从suspend中返回 /* * Wait for the suspend/resume to complete. If there are * pending acknowledges, we wait here for them. * * Note that we need to ensure that the PM subsystem does * not kick us out of the wait when it suspends the threads. */ flags = current-flags; current-flags |= PF_NOFREEZE; /* * Note: do not allow a thread which is acking the suspend * to escape until the resume is complete. */ if (as-suspend_state = SUSPEND_ACKED) wait_event(apm_suspend_waitqueue, as-suspend_state = SUSPEND_DONE); else wait_event_interruptible(apm_suspend_waitqueue, as-suspend_state = SUSPEND_DONE); current-flags = flags; err = as-suspend_result; as-suspend_state = SUSPEND_NONE; break; return err;4. 事件队列函数static void queue_event(apm_event_t event, struct apm_user *sender) struct apm_user *as; down_read(&user_list_lock); /将事件加入其他USER,除自己外 list_for_each_entry(as, &apm_user_list, list) if (as != sender & as-reader) queue_event_one_user(as, event); up_read(&user_list_lock); /唤醒等待读的进程 wake_up_interruptible(&apm_waitqueue);static void queue_event_one_user(struct apm_user *as, apm_event_t event) if (as-suser & as-writer) switch (event) case APM_SYS_SUSPEND: case APM_USER_SUSPEND: /* * If this user already has a suspend pending, * dont queue another one. */ if (as-suspend_state != SUSPEND_NONE) return; as-suspend_state = SUSPEND_PENDING; suspends_pending+; break; queue_add_event(&as-queue, event);static void queue_add_event(struct apm_queue *q, apm_event_t event) q-event_head = (q-event_head + 1) % APM_MAX_EVENTS; if (q-event_head = q-event_tail) /满了 static int notified; if (notified+ = 0) printk(KERN_ERR apm: an event queue overflowedn); q-event_tail = (q-event_tail + 1) % APM_MAX_EVENTS; q-eventsq-event_head = event; 加入队头在来看一个出队的函数:/在队尾出列static inline apm_event_t queue_get_event(struct apm_queue *q) q-event_tail = (q-event_tail + 1) % APM_MAX_EVENTS; return q-eventsq-event_tail;/* APM event queue management.*/static inline int queue_empty(struct apm_queue *q) return q-event_head = q-event_tail;/队列的结构/* Maximum number of events stored*/#define APM_MAX_EVENTS 16struct apm_queue unsigned int event_head; unsigned int event_tail; apm_event_t eventsAPM_MAX_EVENTS;5. apm_suspend()这里才是整个设备想做的事情-将系统转入suspend状态static void apm_suspend(void) struct apm_user *as; /调用体系无关的接口,将系统转入suspend状态 int err = pm_suspend(PM_SUSPEND_MEM); /从suspend返回 /* * Anyone on the APM queues will think were still suspended. * Send a message so everyone knows were now awake again. */ /发送一个resume事件 queue_event(APM_NORMAL