Android休眠唤醒驱动流程分析(二)

在suspend_freeze_processes()函数中调用了freeze_processes()函数，而freeze_processes()函数中又调用了try_to_freeze_tasks()来完成冻结任务。在冻结过程中，会判断当前进程是否有wake_lock，若有，则冻结失败，函数会放弃冻结。

static int try_to_freeze_tasks(bool sig_only)

{

struct task_struct *g, *p;

unsigned long end_time;

unsigned int todo;

struct timeval start, end;

u64 elapsed_csecs64;

unsigned int elapsed_csecs;

unsigned int wakeup = 0;

do_gettimeofday(&start);

end_time = jiffies + TIMEOUT;

do {

todo = 0;

read_lock(&tasklist_lock);

do_each_thread(g, p) {

if (frozen(p) || !freezeable(p))

continue;

if (!freeze_task(p, sig_only))

continue;

if (!task_is_stopped_or_traced(p) &&

!freezer_should_skip(p))

todo++;

} while_each_thread(g, p);

read_unlock(&tasklist_lock);

yield();

if (todo && has_wake_lock(WAKE_LOCK_SUSPEND)) {

wakeup = 1;

break;

}

if (time_after(jiffies, end_time))

break;

} while (todo);

do_gettimeofday(&end);

elapsed_csecs64 = timeval_to_ns(&end) - timeval_to_ns(&start);

do_div(elapsed_csecs64, NSEC_PER_SEC / 100);

elapsed_csecs = elapsed_csecs64;

if (todo) {

if(wakeup) {

printk("\n");

printk(KERN_ERR "Freezing of %s aborted\n",

sig_only ? "user space " : "tasks ");

}

else {

printk("\n");

printk(KERN_ERR "Freezing of tasks failed after %d.d seconds "

"(%d tasks refusing to freeze):\n",

elapsed_csecs / 100, elapsed_csecs % 100, todo);

show_state();

}

read_lock(&tasklist_lock);

do_each_thread(g, p) {

task_lock(p);

if (freezing(p) && !freezer_should_skip(p))

printk(KERN_ERR " %s\n", p->comm);

cancel_freezing(p);

task_unlock(p);

} while_each_thread(g, p);

read_unlock(&tasklist_lock);

} else {

printk("(elapsed %d.d seconds) ", elapsed_csecs / 100,

elapsed_csecs % 100);

}

return todo ? -EBUSY : 0;

}

到现在，所有的进程(也包括workqueue/kthread) 都已经停止了，内核态进程有可能在停止的时候握有一些信号量，所以如果这时候在外设里面去解锁这个信号量有可能会发生死锁， 所以在外设suspend()函数里面作lock/unlock锁要非常小心，建议不要在外设的suspend()里面等待锁。而且suspend的过程中，有一些log是无法输出的，所以一旦出现问题，非常难调试。

回到enter_state()函数中，再冻结进程完成后，调用suspend_devices_and_enter()函数让外设进入休眠。该函数中，首先休眠串口（之后不能再显示log，解决方法为在kernel配置选项的cmd_line中，添加”no_console_suspend”选项），再通过device_suspend()函数调用各驱动的suspend函数。

当外设进入休眠后，suspend_ops->prepare()被调用，suspend_ops是板级的PM操作(本文中粉红色的函数，依赖于具体的平台)，以s3c6410为例，其注册在linux_source/arch/arm/plat-s3c64xx/pm.c中，只定义了suspend_ops->enter()函数。

static struct platform_suspend_ops s3c6410_pm_ops = {

.enter = s3c6410_pm_enter,

.valid = suspend_valid_only_mem,

};

接下来，多CPU中的非启动CPU被关闭。

int suspend_devices_and_enter(suspend_state_t state)

{

int error;

if (!suspend_ops)

return -ENOSYS;

if (suspend_ops->begin) {

error = suspend_ops->begin(state);

if (error)

goto Close;

}

suspend_console();

suspend_test_start();

error = device_suspend(PMSG_SUSPEND);

if (error) {

printk(KERN_ERR "PM: Some devices failed to suspend\n");

goto Recover_platform;

}

suspend_test_finish("suspend devices");

if (suspend_test(TEST_DEVICES))

goto Recover_platform;

if (suspend_ops->prepare) {

error = suspend_ops->prepare();

if (error)

goto Resume_devices;

}

if (suspend_test(TEST_PLATFORM))

goto Finish;

error = disable_nonboot_cpus();

if (!error && !suspend_test(TEST_CPUS))

suspend_enter(state);

enable_nonboot_cpus();

Finish:

if (suspend_ops->finish)

suspend_ops->finish();

Resume_devices:

suspend_test_start();

device_resume(PMSG_RESUME);

suspend_test_finish("resume devices");

resume_console();

Close:

if (suspend_ops->end)

suspend_ops->end();

return error;

Recover_platform:

if (suspend_ops->recover)

suspend_ops->recover();

goto Resume_devices;

}

接下来suspend_enter()被调用，该函数首先关闭IRQ，然后调用device_power_down(), 它会调用suspend_late()函数, 这个函数是系统真正进入休眠最后调用的函数, 通常会在这个函数中作最后的检查，接下来休眠所有的系统设备和总线。最后调用 suspend_pos->enter() 来使CPU进入省电状态。这时候，整个休眠过程完成，代码的执行也就停在这里了。

static int suspend_enter(suspend_state_t state)

{

int error = 0;

device_pm_lock();

#ifdef CONFIG_CPU_FREQ

cpufreq_get_cpufreq_name(0);

strcpy(governor_name, cpufreq_governor_name);

if(strnicmp(governor_name, userspace_governor, CPUFREQ_NAME_LEN)) {

cpufreq_set_policy(0, "performance");

}

#endif

arch_suspend_disable_irqs();

BUG_ON(!irqs_disabled());

if ((error = device_power_down(PMSG_SUSPEND))) {

printk(KERN_ERR "PM: Some devices failed to power down\n");

goto Done;

}

error = sysdev_suspend(PMSG_SUSPEND);

if (!error) {

if (!suspend_test(TEST_CORE))

error = suspend_ops->enter(state);

sysdev_resume();

}

device_power_up(PMSG_RESUME);

Done:

arch_suspend_enable_irqs();

#ifdef CONFIG_CPU_FREQ

if(strnicmp(governor_name, userspace_governor, CPUFREQ_NAME_LEN)) {

cpufreq_set_policy(0, governor_name);

}

#endif

BUG_ON(irqs_disabled());

device_pm_unlock();

return error;

}

在suspend_pos->enter()所对应的函数中，代码最终停止在pm_cpu_sleep();处。

static int s3c6410_pm_enter(suspend_state_t state)

{

……

s3c6410_pm_do_save(gpio_save, ARRAY_SIZE(gpio_save));

s3c6410_pm_do_save(irq_save, ARRAY_SIZE(irq_save));

s3c6410_pm_do_save(core_save, ARRAY_SIZE(core_save));

s3c6410_pm_do_save(sromc_save, ARRAY_SIZE(sromc_save));

__raw_writel(__raw_readl(S3C_WAKEUP_STAT), S3C_WAKEUP_STAT);

#ifdef CONFIG_MACH_SMDK6410

__raw_writel(0xffffff00, S3C_NORMAL_CFG);

__raw_writel(0xffffffff, S3C_HCLK_GATE);

__raw_writel(0xffffffff, S3C_PCLK_GATE);

__raw_writel(0xffffffff, S3C_SCLK_GATE);

……

if (s3c6410_cpu_save(regs_save) == 0) {

flush_cache_all();

pm_cpu_sleep();

}

cpu_init();

__raw_writel(s3c_eint_mask_val, S3C_EINT_MASK);

s3c6410_pm_do_restore_core(core_save, ARRAY_SIZE(core_save));

s3c6410_pm_do_restore(sromc_save, ARRAY_SIZE(sromc_save));

……

}