[Pi 5] Device tree files provided in this repo cannot expose debug serial port to chain-booted u-boot

[chaserhkj]

I was trying to get to u-boot prompt and do some hacking with uefi bootloaders and kernel on my RPi 5, so I set up for a minimal environment to get to u-boot prompts on the 3-pin JST connector debug port.

Boot partition content:

bcm2712-rpi-5-b.dtb  config.txt  u-boot.bin

My u-boot is compiled with rpi_arm64_defconf

config.txt content:

arm_64bit=1
kernel=u-boot.bin

However it seems that with device tree files provided in this repo I could not get the console prompt from u-boot. Serial output stuck at

NOTICE:  BL31: v2.6(release):v2.6-240-gfc45bc492
NOTICE:  BL31: Built : 12:55:13, Dec  4 2024

Further examination shows that some hardware devices were initialized correctly but some are not, since when I connected a monitor it showed a u-boot logo correctly. Also when I get the SD card out and check contents again, the u-boot uefi var file ubootefi.var has been created on the boot partition, signalling that u-boot is somewhat working.

I then tested u-boot compiled with CONFIG_SERIAL_PROBE_ALL=y, CONFIG_REQUIRE_SERIAL_CONSOLE=y. With these u-boot went into a boot loop. I think it's not getting the serial port properly setup from the device tree passed from EEPROM firmware so without a serial console it just tried to reset.

I did a bit more searches and landed upon this mailing list post that has the exact symptom as me. So I downloaded a RPi OS image and extracted the device tree from there and that indeed fixed everything.

I suggest there might be a version drift or file corruption for the device tree file in this repo. But the OS image seems to carry the correct one.

[pelwell]

Raspberry Pi do not use U-boot or provide support for it. However, if there is a bug in our firmware, kernel or Device Tree that is shown up by U-boot, we will investigate and try to fix it.