[RK3399][Android7.1] 系统reboot mode机制小结

Platform: RK3399
OS: Android 7.1
Kernel: v4.4.83

背景：

到kernel 4.4上面，发现内核把重启参数通用驱动也实现了。
rk3288 android6.0 kernel3.10上rk是自己实现的。

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文档说明：

针对通用reboot mode驱动，内核有文档解释：

Generic reboot mode core map driver
This driver get reboot mode arguments and call the write interface to stores the magic value in special register or ram . Then the bootloader can read it and take different action according the argument stored.
All mode properties are vendor specific, it is a indication to tell the bootloder what to do when the system reboot, and should be named as mode-xxx = <magic> (xxx is mode name).
- mode-normal: Normal reboot mode, system reboot with command "reboot".
- mode-recovery: Android Recovery mode, it is a mode to format the device or update a new image.
- mode-bootloader: Android fastboot mode, it's a mode to re-flash partitions on the Android based device.
- mode-loader: A bootloader mode, it's a mode used to download image on Rockchip platform, usually used in development.

大概意思就是：
1. reboot mode只提供驱动框架，具体写进去的参数和vendor对应平台相关，重启后会在uboot中判断。
2. 如果模式支持，只要在dts中加上mode-的选项就可以了。

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rk3399平台驱动：

dts配置：
rk3399.dtsi:

reboot-mode {
    compatible = "syscon-reboot-mode";
    offset = <0x300>;
    mode-bootloader = <BOOT_BL_DOWNLOAD>;
    mode-charge = <BOOT_CHARGING>;
    mode-fastboot = <BOOT_FASTBOOT>;
    mode-loader = <BOOT_BL_DOWNLOAD>;
    mode-normal = <BOOT_NORMAL>;
    mode-recovery = <BOOT_RECOVERY>;
    mode-ums = <BOOT_UMS>;
    mode-wipedata = <BOOT_UMS>;
};

reboot mode注册：

syscon_reboot_mode_probe ->
  reboot_mode_register ->
    register_reboot_notifier -> //reboot_notifier的callback是reboot_mode_notify
      blocking_notifier_chain_register  //list是reboot_notifier_list

reboot调用：
当系统重启的时候会调用

kernel_restart -> 
  kernel_restart_prepare ->
    blocking_notifier_call_chain -> 
      __blocking_notifier_call_chain -> 
        notifier_call_chain -> 
          nb->notifier_call -> //reboot_notifier_list被调用到
            reboot_mode_notify -> reboot-mode.c
              get_reboot_mode_magic -> //获取参数对应的magic
                reboot->write ->
                  syscon_reboot_mode_write ->
                    regmap_update_bits //使用regmap mmio更新到寄存器中

重启开机判断是在uboot中完成的

static void fbt_handle_reboot(const char *cmdbuf)
{
    if (!strcmp(&cmdbuf[6], "-bootloader")) {
        FBTDBG("%s\n", cmdbuf);
        board_fbt_set_reboot_type(FASTBOOT_REBOOT_BOOTLOADER);
    }
    if (!strcmp(&cmdbuf[6], "-recovery")) {
        FBTDBG("%s\n", cmdbuf);
        board_fbt_set_reboot_type(FASTBOOT_REBOOT_RECOVERY);
    }
    if (!strcmp(&cmdbuf[6], "-recovery:wipe_data")) {
        FBTDBG("%s\n", cmdbuf);
        board_fbt_set_reboot_type(FASTBOOT_REBOOT_RECOVERY_WIPE_DATA);
    }

    strcpy(priv.response, "OKAY");
    priv.flag |= FASTBOOT_FLAG_RESPONSE;
    fbt_handle_response();
    udelay(1000000); /* 1 sec */

    do_reset(NULL, 0, 0, NULL);
}