Garbage UART output on RPI 4 with upstream kernel DTB

[Stefan Wahren]

Am 20.12.19 um 14:58 schrieb Stefan Wahren:
> Hi,
>
> i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with
> bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see
> garbage on the debug UART (pin 14 & 15). Using the DTB from the
> downstream kernel has a proper UART output. The config.txt contains
> debug_uart=1
>
> I compared both and identified an offending Linux commit:
> ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
>
> Unfortunately reverting this patch still doesn't fix the issue. Any ideas?

After hours of playing with the DTB, i finally found the reason why the
upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be
compiled with flag "-@".

It isn't clear to me, why this is necessary but it would be nice to make
U-Boot work without this.

Regards
Stefan

>
> Best regards
> Stefan
>
>