Hi Matthias,
Yes it is. I was working on this the last weeks and just posted the patches today. Would be nice if you could test and provide feedback :)
The patch works for me on Raspberry PI 4B 1GB and a Raspberry PI 3B v1.2 (BCM2837RIFBG) when applied to dfd590075c and using the rpi_4_defconfig I am able to boot to Linux via grub2 on both boards with the same u-boot.bin.
I did run into a couple of little problems though:
1. On the PI 4 with mainline u-boot the screen turns yellow and wraps around on itself a second or so into the linux boot (grub screen is fine). With the patch applied I get the same behaviour on the PI3. Everything still works the screen is just messed up.
If I instead use rpi_3_defconfig, I get a rainbow screen on the PI4 and the screen goes switches off instead of just turning yellow on the PI3.
2. USB wireless keyboard doesn't work until Linux loads on both systems if built with rpi_4_defconfig. I tried copying settings from rpi_3_defconfig[1] but then keyboard didn't work on either system.
Anyways, this is great thanks for fixing this.
Cheers, Geoff
[1] CONFIG_PREBOOT="usb start" CONFIG_CMD_USB=y CONFIG_USB=y CONFIG_DM_USB=y CONFIG_USB_DWC2=y CONFIG_USB_KEYBOARD=y CONFIG_USB_HOST_ETHER=y CONFIG_USB_ETHER_LAN78XX=y CONFIG_USB_ETHER_SMSC95XX=y