树莓派4从USB启动

$ uname -a
Linux raspberrypi 5.4.83-v7l+ #1379 SMP Mon Dec 14 13:11:54 GMT 2020 armv7l GNU/Linux

$ sudo rpi-eeprom-update
BCM2711 detected
Dedicated VL805 EEPROM detected
*** UPDATE AVAILABLE ***
BOOTLOADER: update available
CURRENT: Mon 15 Jul 12:59:55 UTC 2019 (1563195595)
 LATEST: Thu  3 Sep 12:11:43 UTC 2020 (1599135103)
 FW DIR: /lib/firmware/raspberrypi/bootloader/critical
VL805: update available
CURRENT: 00013701
 LATEST: 000138a1

$ sudo rpi-eeprom-update -a
BCM2711 detected
Dedicated VL805 EEPROM detected
*** INSTALLING EEPROM UPDATES ***
BOOTLOADER: update available
CURRENT: Mon 15 Jul 12:59:55 UTC 2019 (1563195595)
 LATEST: Thu  3 Sep 12:11:43 UTC 2020 (1599135103)
 FW DIR: /lib/firmware/raspberrypi/bootloader/critical
VL805: update available
CURRENT: 00013701
 LATEST: 000138a1
BOOTFS /boot
EEPROM updates pending. Please reboot to apply the update.

$ sudo reboot

参考: https://www.raspberrypi.org/documentation/hardware/raspberrypi/booteeprom.md