Serial console input dead after successfully booting buildroot system on rpi4

[Matthias]

Hi,

after using the u-boot (v2022.01) bootloader built with rpi_4_32b_defconfig on a buildroot 2022.05 custom system, I can no longer input on the serial console connected to an FTDI adapter wired to Pins 8/10 of the RPi4 GPIO pin header.

Here's what I did:

* Replaced kernel=zImage by kernel=u-boot.bin in config.txt
* Copied u-boot.bin to the boot partition
* On the u-boot prompt:
  u-boot> fatload mmc 0:1 ${kernel_addr_r} zImage
  u-boot> fatload mmc 0:1 ${fdt_addr_r} ${fdtfile}
  u-boot> setenv bootargs console=tty1 console=ttyAMA0,115200 root=/dev/mmcblk0p2 rootwait
  u-boot> bootz ${kernel_addr_r} - ${fdt_addr_r}

The system boots up fine and is fully functional. Messages keep getting printed to the serial console but no input is received, e.g. login is not possible. Logging on via SSH works fine. When starting up the system by means of kernel=zImage directly the problem does not occur.

Any idea what might be the reason?