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android 5.0关机流程-kernel层

韩恺
2023-12-01

前面已经讲到了lowLevelShutdown()与lowLevelReboot()都在PowerManagerService.java实现,都只是设置一个属性:SystemProperties.set(sys.powerctl, xxx);这里从这继续往下讲:

sys.powerctl属性触发开关在init.rc定义:

on property:sys.powerctl=*                                                    
        powerctl ${sys.powerctl}

on property:sys.powerctl=*表示当属性sys.powerctl设置为任何值是都会跑到这里,触发动作是powerctl ${sys.powerctl},这个动作的意思是调用powerctl指令,并把sys.powerctl的值传给它。powerctl指令在init进程会执行。

从下面的表可知,powerctl对应的操作是do_powerctl

[system/core/init/keywords.h]

KEYWORD(powerctl,    COMMAND, 1, do_powerctl)

do_powerctl的实现代码如下:

 794 int do_powerctl(int nargs, char **args)
 795 {
 796     char command[PROP_VALUE_MAX];
 797     int res;
 798     int len = 0;
 799     int cmd = 0;
 800     char *reboot_target;
 801 
 802     res = expand_props(command, args[1], sizeof(command));
 803     if (res) {
 804         ERROR("powerctl: cannot expand '%s'\n", args[1]);
 805         return -EINVAL;
 806     }
 807 
 808     if (strncmp(command, "shutdown", 8) == 0) {
 809         cmd = ANDROID_RB_POWEROFF;
 810         len = 8;
 811     } else if (strncmp(command, "reboot", 6) == 0) {
 812         cmd = ANDROID_RB_RESTART2;
 813         len = 6;
 814     } else {
 815         ERROR("powerctl: unrecognized command '%s'\n", command);
 816         return -EINVAL;
 817     }
 818 
 819     if (command[len] == ',') {
 820         reboot_target = &command[len + 1];
 821     } else if (command[len] == '\0') {
 822         reboot_target = "";
 823     } else {
 824         ERROR("powerctl: unrecognized reboot target '%s'\n", &command[len]);
 825         return -EINVAL;
 826     }
 827 
 828     return android_reboot(cmd, 0, reboot_target);
 829 }

可以看到最后其调用的是android_reboot()函数,其实现如下:

107 int android_reboot(int cmd, int flags UNUSED, char *arg)
108 {
109     int ret;
110 
111     sync();
112     remount_ro();
113 
114     switch (cmd) {
115         case ANDROID_RB_RESTART:
116             ret = reboot(RB_AUTOBOOT);
117             break;
118 
119         case ANDROID_RB_POWEROFF:
120             ret = reboot(RB_POWER_OFF);
121             break;
122 
123         case ANDROID_RB_RESTART2:
124             ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
125                            LINUX_REBOOT_CMD_RESTART2, arg);
126             break;
127 
128         default:
129             ret = -1;
130     }
131 
132     return ret;
133 }
可以看到如果是系统关机会走ANDROID_RB_POWEROFF分支,而重启则会走ANDROID_RB_RESTART2分支,sync() 回写block设备的内容,这是阻塞型操作;remount_ro() 把block设备remount成ro,这里有个关键LOG:SysRq : Emergency Remount R/O,这是在logkit所能看到的最后一句LOG,因为remount成ro了,后面的LOG要通过last kmsg技术导出来。syscall(__NR_reboot....直接调用了linux的__NR_reboot系统调用,这点与android KK不同,这边直接用syscall功能,KK则通过汇编。先看看reboot()的实现代码:

[bionic/libc/bionic/reboot.cpp]

 32 extern "C" int __reboot(int, int, int, void*);
 33 
 34 int reboot(int mode) {
 35   return __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, NULL);
 36 }

调用了__reboot,它在汇编实现 如下:
[bionic/libc/arch-arm/syscalls/__reboot.S]

  3 #include <private/bionic_asm.h>
  4 
  5 ENTRY(__reboot)
  6     mov     ip, r7
  7     ldr     r7, =__NR_reboot  //也用到了__NR_reboot系统调用
  8     swi     #0
  9     mov     r7, ip
 10     cmn     r0, #(MAX_ERRNO + 1)
 11     bxls    lr
 12     neg     r0, r0
 13     b       __set_errno_internal
 14 END(__reboot)

__NR_reboot对应的内核入口在哪里?

[bionic/libc/kernel/uapi/asm-generic/unistd.h]

221 #define __NR_reboot 142 

它在内核入口如下:
bionic/libc/kernel/uapi/asm-generic/unistd.h与kernel/include/uapi/asm-generic/unistd.h是对应的,方便以后代码追踪,

来看看kernel下的[kernel/include/uapi/asm-generic/unistd.h]

422 #define __NR_reboot 142                                                                                                                                                                                  
423 __SYSCALL(__NR_reboot, sys_reboot)

可以看到__NR_reboot 映射到 sys_reboot,他的声明在kernel/include/linux/syscall.h中

asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd,
				void __user *arg);

sys_reboot而最后的定义是在kernel/kernel/sys.c中

SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
		void __user *, arg){
	struct pid_namespace *pid_ns = task_active_pid_ns(current);
	char buffer[256];
	int ret = 0;

	printk(KERN_EMERG "[shutdown_debug] enter reboot syscall.\n");

	/* We only trust the superuser with rebooting the system. */
	if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT)) {
		printk(KERN_EMERG "[shutdown_debug] ns_capable return,pid_ns->user_ns=0x%x.\n",pid_ns->user_ns);
		return -EPERM;
	}

	/* For safety, we require "magic" arguments. */
	if (magic1 != LINUX_REBOOT_MAGIC1 ||
	    (magic2 != LINUX_REBOOT_MAGIC2 &&
	                magic2 != LINUX_REBOOT_MAGIC2A &&
			magic2 != LINUX_REBOOT_MAGIC2B &&
	                magic2 != LINUX_REBOOT_MAGIC2C)) {
		printk(KERN_EMERG "[shutdown_debug] magic return.magic1=%d,magic2=%d\n",magic1,magic2);
		return -EINVAL;
	}

	/*
	 * If pid namespaces are enabled and the current task is in a child
	 * pid_namespace, the command is handled by reboot_pid_ns() which will
	 * call do_exit().
	 */
	ret = reboot_pid_ns(pid_ns, cmd);
	if (ret) {
		printk(KERN_EMERG "[shutdown_debug] reboot_pid_ns return,ret=%d.\n",ret);
		return ret;
	}

	/* Instead of trying to make the power_off code look like
	 * halt when pm_power_off is not set do it the easy way.
	 */
	if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)
		cmd = LINUX_REBOOT_CMD_HALT;

	mutex_lock(&reboot_mutex);
	switch (cmd) {
	case LINUX_REBOOT_CMD_RESTART:
		kernel_restart(NULL);
		break;

	case LINUX_REBOOT_CMD_CAD_ON:
		C_A_D = 1;
		break;

	case LINUX_REBOOT_CMD_CAD_OFF:
		C_A_D = 0;
		break;

	case LINUX_REBOOT_CMD_HALT:
		kernel_halt();
		do_exit(0);
		panic("cannot halt");

	case LINUX_REBOOT_CMD_POWER_OFF:
		kernel_power_off();
		do_exit(0);
		break;

	case LINUX_REBOOT_CMD_RESTART2:
		if (strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) < 0) {
			ret = -EFAULT;
			break;
		}
		buffer[sizeof(buffer) - 1] = '\0';

		kernel_restart(buffer);
		break;

#ifdef CONFIG_KEXEC
	case LINUX_REBOOT_CMD_KEXEC:
		ret = kernel_kexec();
		break;
#endif

#ifdef CONFIG_HIBERNATION
	case LINUX_REBOOT_CMD_SW_SUSPEND:
		ret = hibernate();
		break;
#endif

	default:
		ret = -EINVAL;
		break;
	}
	mutex_unlock(&reboot_mutex);
	printk(KERN_EMERG "[shutdown_debug] exit reboot syscall.\n");
	return ret;
}

那么SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd, void __user *, arg)是如何转换成asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd, void __user *arg);形式的呢?其实就是宏的一些基本用法而已,我们来简单分析一下。在include/linux/syscall.h里有下面一组宏:

#define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE4(name, ...) SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)

这里每个SYSCALL_DEFINE后面的数字说明了,名为name的系统调用接收几个输入参数。这些宏都由一个基础宏SYSCALL_DEFINEx来实现:

#define SYSCALL_DEFINEx(x, sname, ...)				\
	SYSCALL_METADATA(sname, x, __VA_ARGS__)			\
	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)

#define __SYSCALL_DEFINEx(x, name, ...)					\
	asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
	static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
	asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__))	\
	{								\
		long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__));	\
		__MAP(x,__SC_TEST,__VA_ARGS__);				\
		__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__));	\
		return ret;						\
	}								\
	SYSCALL_ALIAS(sys##name, SyS##name);				\
	static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))

到此sys_reboot系统调用在kernel中从SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd, void __user *, arg)开始往下执行:

这个函数有很多分支,我们只关心kernel_power_off()和kernel_restart()两函数就行:

void kernel_power_off(void)
{
	printk(KERN_EMERG "[shutdown_debug] enter kernel_power_off.\n");
	kernel_shutdown_prepare(SYSTEM_POWER_OFF); //关闭外设
	if (pm_power_off_prepare)
		pm_power_off_prepare();
	migrate_to_reboot_cpu();
	syscore_shutdown(); //关闭syscore
	printk(KERN_EMERG "Power down.\n");//关键打印
	kmsg_dump(KMSG_DUMP_POWEROFF); 
	machine_power_off();
	printk(KERN_EMERG "[shutdown_debug] exit kernel_power_off.\n");
}

void kernel_restart(char *cmd)
{
	kernel_restart_prepare(cmd);//关闭外设
	migrate_to_reboot_cpu();
	syscore_shutdown();//关闭syscore
	if (!cmd)
		printk(KERN_EMERG "Restarting system.\n");//关键打印
	else
		printk(KERN_EMERG "Restarting system with command '%s'.\n", cmd);
	kmsg_dump(KMSG_DUMP_RESTART);
	preempt_disable();
	machine_restart(cmd);
}

都执行XX_prepare()函数:

static void kernel_shutdown_prepare(enum system_states state)
{
	printk(KERN_EMERG "[shutdown_debug] enter kernel_shutdown_prepare.\n");
	blocking_notifier_call_chain(&reboot_notifier_list,
		(state == SYSTEM_HALT)?SYS_HALT:SYS_POWER_OFF, NULL);
	system_state = state;
	usermodehelper_disable();
	device_shutdown();
	printk(KERN_EMERG "[shutdown_debug] exit kernel_shutdown_prepare.\n");
}

void kernel_restart_prepare(char *cmd)
{
	blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd);
	system_state = SYSTEM_RESTART;
	usermodehelper_disable();
	device_shutdown();
}

除了前面不同,都调用了device_shutdown()函数,关闭外设。

machine_power_off() machine_resestart()函数实现:

void machine_power_off(void)
{
	smp_send_stop();

	if (pm_power_off)
		pm_power_off();//关机
}

void machine_restart(char *cmd)
{
	smp_send_stop();

	/* Flush the console to make sure all the relevant messages make it
	 * out to the console drivers */
	arm_machine_flush_console();

	arm_pm_restart(reboot_mode, cmd);//重启

	/* Give a grace period for failure to restart of 1s */
	mdelay(1000);

	/* Whoops - the platform was unable to reboot. Tell the user! */
	printk("Reboot failed -- System halted\n");
	local_irq_disable();
	while (1);
}
pm_power_offf() arm_pm_restart()都是一个函数指针,他们的复制,根据厂家的不同而不同,SPRD,mediatek,msm三家各有各的操作,这里是SPRD,其赋值位于kernel/drivers/platform/sprd/Pm-scx35.c:
void __init sc_pm_init(void)
{
	
	init_reset_vector();
	pm_power_off   = sc8830_power_off;
	arm_pm_restart = sc8830_machine_restart;
	pr_info("power off %pf, restart %pf\n", pm_power_off, arm_pm_restart);
	init_gr();
	setup_autopd_mode();
	pm_ana_ldo_config();
	init_led();
	/* disable all sleep mode */
	sci_glb_clr(REG_AP_AHB_MCU_PAUSE, BIT_MCU_DEEP_SLEEP_EN | BIT_MCU_LIGHT_SLEEP_EN | \
		BIT_MCU_SYS_SLEEP_EN | BIT_MCU_CORE_SLEEP);
	set_reset_vector();
#ifdef CONFIG_DDR_VALIDITY_TEST
	test_memory();
#endif
#ifndef CONFIG_SPRD_PM_DEBUG
	pm_debug_init();
#endif

	/* enable arm clock auto gating*/
	//sci_glb_set(REG_AHB_AHB_CTL1, BIT_ARM_AUTO_GATE_EN);
#ifdef CONFIG_CPU_IDLE
	sc_cpuidle_init();
#endif
/*
	wake_lock_init(&pm_debug_lock, WAKE_LOCK_SUSPEND, "pm_not_ready");
	wake_lock(&pm_debug_lock);
*/
#if defined(CONFIG_SPRD_DEBUG)
	sprd_debug_init();
#endif
}

其实现如下:

static void sc8830_power_off(void)
{
	u32 reg_val;
	/*turn off all modules's ldo*/

#ifdef CONFIG_SPRD_EXT_IC_POWER
	sprd_extic_otg_power(0);
#endif
	sci_adi_raw_write(ANA_REG_GLB_LDO_PD_CTRL, 0x1fff);

#if defined(CONFIG_ARCH_SCX15) || defined(CONFIG_ADIE_SC2723) || defined(CONFIG_ADIE_SC2723S)
	sci_adi_raw_write(ANA_REG_GLB_PWR_WR_PROT_VALUE,BITS_PWR_WR_PROT_VALUE(0x6e7f));
	do{
		reg_val = (sci_adi_read(ANA_REG_GLB_PWR_WR_PROT_VALUE) & BIT_PWR_WR_PROT);
	}while(reg_val == 0);
	sci_adi_raw_write(ANA_REG_GLB_LDO_PD_CTRL,0xfff);
	sci_adi_raw_write(ANA_REG_GLB_LDO_DCDC_PD,0x7fff);
#endif
#if defined(CONFIG_ADIE_SC2713S) || defined(CONFIG_ADIE_SC2713)
	/*turn off system core's ldo*/
	sci_adi_raw_write(ANA_REG_GLB_LDO_DCDC_PD_RTCCLR, 0x0);
	sci_adi_raw_write(ANA_REG_GLB_LDO_DCDC_PD_RTCSET, 0X7fff);
#endif
}

static void sc8830_machine_restart(char mode, const char *cmd)
{
	local_irq_disable();
	local_fiq_disable();

	arch_reset(mode, cmd);

	mdelay(1000);

	printk("reboot failed!\n");

	while (1);
}

至此,kernel的关机流程运行完毕!





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