@大法师 感谢！完美解决我的问题！

已找到/dev/input/js0

更新内核方法在下面，方便其他新手朋友操作
https://www.cool-pi.com/topic/131/coolpi-4b-linux-kernel开发在线更新说明

@AugustRobot_Zou said in How to upgrade the boot loader of coolpi 4b？:

Since I upgraded my PC to Win11, the RKDevTool always cannot find the device of coolpi-4b.
Does the RKDevTool support Win11?
Or could I upgrade the boot loader of coolpi-4b in ubuntu environment?

https://www.cool-pi.com/topic/47/coolpi-4b-bootloader命令行升级方法

用这个办法升级成功，避开RKDevTool 在win11驱动问题

@大法师 更新情况！

还是使用不了，会出现 Couldn't open Joystick /dev/input/js0的报错。

经过google后解决：
https://forums.developer.nvidia.com/t/couldnt-open-joystick-dev-input-js0-solved/65192

帖子说需要多编译一个CONFIG_JOYSTICK_XPAD=y

于是我搜索后，发现rockchip_defconfig里面有三行
ONFIG_JOYSTICK_XPAD=y
CONFIG_JOYSTICK_XPAD_FF=y
CONFIG_JOYSTICK_XPAD_LEDS=y

我也不管，全部复制进rk3588s_cp4b_defconfig，重新编译后，更新内核可以成功。

@大法师 谢谢！搞定了
ubuntu 20没有/etc/rc.local，需要

1. 新建service
   sudo vim /etc/systemd/system/rc-local.service

[Unit]
 Description=/etc/rc.local Compatibility
 ConditionPathExists=/etc/rc.local
[Service]
 Type=forking
 ExecStart=/etc/rc.local start
 TimeoutSec=0
 StandardOutput=tty
 RemainAfterExit=yes
 SysVStartPriority=99
[Install]
 WantedBy=multi-user.target

2.使能service
sudo systemctl enable rc-local.service
3.新建/etc/rc.local
sudo vim /etc/rc.local
并需要操作的命令加进去
4.启动服务
sudo systemctl start rc-local.service
sudo systemctl status rc-local.service