android restart reason機制

Reboot傳遞參數,使得開機進入參數固定的模式（通常有我們熟悉的bootloader和recovery等），本質是在kernel shutdown時會調用到restart，

將模式數值寫到share memory中，那麼在開機bootloader階段，再去讀取這塊內存，boot進入指定的模式，要是匹配不起來就正常boot,以下是貼出的代碼；

restart 2種方式：

a: android_reboot(ANDROID_RB_RESTART2, 0, "rtcalarm");//進入rtc alarm模式

b: adb reboot bootloader,adb reboot recovery; //進入我們熟悉的bootloader和recorevy模式

Restar.c:

void *restart_reason;

/*函數將被賦值給machine restart指針*/

void msm_restart(char mode, const char *cmd)

{

#ifdef CONFIG_MSM_DLOAD_MODE

/* This looks like a normal reboot at this point. */

set_dload_mode(0);

/* Write download mode flags if we're panic'ing */

set_dload_mode(in_panic);

/* Write download mode flags if restart_mode says so */

if (restart_mode == RESTART_DLOAD) {

set_dload_mode(1);

#ifdef CONFIG_LGE_CRASH_HANDLER

writel(0x6d63c421, restart_reason);

goto reset;

#endif

}

/* Kill download mode if master-kill switch is set */

if (!download_mode)

set_dload_mode(0);

#endif

printk(KERN_NOTICE "Going down for restart now\n");

pm8xxx_reset_pwr_off(1);

if (cmd != NULL) {

if (!strncmp(cmd, "bootloader", 10)) {

__raw_writel(0x77665500, restart_reason);

} else if (!strncmp(cmd, "recovery", 8)) {

__raw_writel(0x77665502, restart_reason);

} else if (!strncmp(cmd, "oem-", 4)) {

unsigned long code;

code = simple_strtoul(cmd + 4, NULL, 16) & 0xff;

__raw_writel(0x6f656d00 | code, restart_reason);

} else {

__raw_writel(0x77665501, restart_reason);

}

} else {

__raw_writel(0x77665501, restart_reason);

}

#ifdef CONFIG_LGE_CRASH_HANDLER

if (in_panic == 1)

set_kernel_crash_magic_number();

reset:

#endif /* CONFIG_LGE_CRASH_HANDLER */

__raw_writel(0, msm_tmr0_base + WDT0_EN);

if (!(machine_is_msm8x60_fusion() || machine_is_msm8x60_fusn_ffa())) {

mb();

__raw_writel(0, PSHOLD_CTL_SU); /* Actually reset the chip */

mdelay(5000);

pr_notice("PS_HOLD didn't work, falling back to watchdog\n");

}

__raw_writel(1, msm_tmr0_base + WDT0_RST);

__raw_writel(5*0x31F3, msm_tmr0_base + WDT0_BARK_TIME);

__raw_writel(0x31F3, msm_tmr0_base + WDT0_BITE_TIME);

__raw_writel(1, msm_tmr0_base + WDT0_EN);

mdelay(10000);

printk(KERN_ERR "Restarting has failed\n");

}

static int __init msm_restart_init(void)

{

#ifdef CONFIG_MSM_DLOAD_MODE

atomic_notifier_chain_register(&panic_notifier_list, &panic_blk);

dload_mode_addr = MSM_IMEM_BASE + DLOAD_MODE_ADDR;

#ifdef CONFIG_LGE_CRASH_HANDLER

lge_error_handler_cookie_addr = MSM_IMEM_BASE +

LGE_ERROR_HANDLER_MAGIC_ADDR;

#endif

set_dload_mode(download_mode);

#endif

msm_tmr0_base = msm_timer_get_timer0_base();

restart_reason = MSM_IMEM_BASE + RESTART_REASON_ADDR;// restart_reason被賦值內存地址

pm_power_off = msm_power_off;

return 0;

}

lk:init.c

/*lk裡面讀出kernel寫入的restart數值*/

unsigned check_reboot_mode(void)

{

unsigned restart_reason = 0;

void *restart_reason_addr = (void *)0x2A05F65C;

/* Read reboot reason and scrub it */

restart_reason = readl(restart_reason_addr);

writel(0x00, restart_reason_addr);

return restart_reason;

}

#define RECOVERY_MODE 0x77665502

#define FASTBOOT_MODE 0x77665500

#define ADB_REBOOT_MODE 0x77665501

/*check reboot mode*/

reboot_mode = check_reboot_mode();

#if CONFIG_CHARING_WHILE_MECHINE_TRUN_OFF

{

extern unsigned int custom_power_on_charger(void);

if(custom_power_on_charger() && reboot_mode && (reboot_mode!=FASTBOOT_MODE) && (reboot_mode != ADB_REBOOT_MODE))

boot_into_recovery=1;

dprintf(0, "[charger] %s() custom_power_on_charger()=%x check_reboot_mode()=%0x\n", __func__, custom_power_on_charger(), reboot_mode);

}

#endif

if (reboot_mode == RECOVERY_MODE) {

boot_into_recovery = 1;

} else if(reboot_mode == FASTBOOT_MODE) {

goto fastboot;

}

那麼熟悉這套機制，我們就可以添加自己的模式了，比如鬧鐘模式，工廠模式等等；