Hi Matthias,
Am 23.12.19 um 21:20 schrieb 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?
i didn't call dtc directly via command line. I just added this Makefile hack [1] to the Linux upstream tree. This will add a __symbols__ section to the DTB which is required for overlays. You can verify this with dtdiff.
Since the upstream kernel boots without the __symbols__ section, i think this garbage output issue could be fixed in u-boot.
Regards Stefan
[1] - https://github.com/raspberrypi/linux/blob/b85f76a63d5f1b13220c61244469d55487...
Regards, Matthias