Hi Stefan, sorry for the delay, answers inside.
On 25/12/2019 14:55, Stefan Wahren wrote: > Am 24.12.19 um 13:38 schrieb Matthias Brugger: >> >> On 24/12/2019 12:56, Stefan Wahren wrote: >>> 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. >>> >> Little by little I grasp what you are doing. So you compile the DTB in the >> kernel, then pass the blob to u-boot and add it with OF_EMBED? Is that >> correct? > > I use a recent Raspbian image, replace the bcm2711 DTB with the upstream > kernel ones (yes build with make dtbs) and kernel7.img with u-boot.bin > (renamed all the other kernel binaries to make sure kernel7.img is > really used). Also use a boot.scr from here, but not sure this have an > influence [1]. I used the rpi_4_32b_defconfig without any modifications > like OF_EMBED. I assume u-boot uses the FDT image passed by the > Raspberry Pi bootloader. Yes exactly, FDT image is taken from the bootloader. Can you please double check your config.txt especially the force_turbo and initial_trubo options. I can see garbage on the serial console when the initial_turbo time is over (when setting force_turbo=0). If I set force_turbo=1 I don't observe this behavior. Regards, Matthias > > [1] - https://andrei.gherzan.ro/linux/uboot-on-rpi/ > >> >> Regards, >> Matthias >
