Fairphone 4: Kernel and GPL sources published

Did anyone have success in making a working rebuild of the Stock kernel? I’m trying to establish a baseline what camera issues on custom ROM are due to kernel or system. Was thinking that I can just use a custom built kernel with stock rom for a start.

I’m following the official guide at Fairphone 4 Kernel Source Code — FAIRPHONE open source documentation

I’m on Stock FP3V version with unlocked bootloader. I’m making a vendor/fp4-perf_defconfig build without apparent issues.

I downloaded stock A.116 boot.img and unpacked that into Image, dtb, and ramdisk. Then rebuilding the image with mkbootimg, keeping dtb and ramdisk but using the new kernel image. Then booting that via fastboot boot boot-custom.img

The kernel boots up, but camera is not working at all. If I just repack the original kernel build everything is working, so somehow the self-built Kernel image must differ.

Can you maybe provide advice? Are the published kernel sources up date?

Also another question I have is where one would obtain the device tree for FP4? I see that /e/OS pulled it in to their kernel from somewhere, but what is the source of that? Why is it not open source at the moment?

This is how I did try to rebuild a boot.img:
mkbootimg --kernel out/kernel --ramdisk out/ramdisk --dtb out/dtb --cmdline "console=ttyMSM0,115200,n8 earlycon=msm_geni_serial,0x888000 androidboot.hardware=qcom androidboot.console=ttyMSM0 androidboot.memcg=1 lpm_levels.sleep_disabled=1 video=vfb:640x400,bpp=32,memsize=3072000 msm_rtb.filter=0x237 service_locator.enable=1 androidboot.usbcontroller=a600000.dwc3 swiotlb=2048 cgroup.memory=nokmem,nosocket loop.max_part=7 buildvariant=user" --os_version 11.0.0 --os_patch_level 2022-04 --header_version 2 --pagesize 4096 --base 0x0 -o test.img

Further testing revealed that stock android works fine if I just flash complete boot.img and dtbo.img from Lineage build. Still curious why just replacing the kernel image breaks some functionality.