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));
……
}