Garbage UART output on RPI 4 with upstream kernel DTB

[Matthias Brugger]

Hi Stefan,

On 23/12/2019 19:51, Stefan Wahren wrote:
> 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.
> 

Can you provide the exact command you are using?

Regards,
Matthias