Raspberry Pi no network after PXE boot with flatcar due to missing kernel

[wernerb]

Description

Support has already been added for RPI4 network in #227 . However, when using PXE booting, we need an additional flag called CONFIG_MDIO_BCM_UNIMAC. More details can be found here https://bugzilla.redhat.com/show_bug.cgi?id=1943983

Impact

No ethernet adapter when network booting (either PXE or UEFI HTTP).

Environment and steps to reproduce

boot http://boot.netboot.xyz/ipxe/netboot.xyz-arm64.efi manually through the HTTP Network boot gui with the UEFI firmware for
RPI4.
Then when booted into the menu.
Select Execute iPXE shell

Type in the following:

kernel https://alpha.release.flatcar-linux.net/arm64-usr/current/flatcar_production_pxe.vmlinuz initrd=flatcar_production_pxe_image.cpio.gz flatcar.config.url=http://urldoesntmatter flatcar.first_boot=yes console=tty0 console=ttyS0 flatcar.autologin
initrd https://alpha.release.flatcar-linux.net/arm64-usr/current/flatcar_production_pxe_image.cpio.gz
boot

You will see messages such as:

[  133.316150] Unable to find mii
[  133.319239] bcmgenet BCM6E4E:00 enabcm6e4ei0: failed to connect to PHY

Expected behavior
The network driver comes up.

Additional information
Enabling the flag would fix the support for PXE alongside the support already #227

[dongsupark]

Thanks for the PR flatcar-archive/coreos-overlay#929.
From my understanding, we would have to also update dracut to >= 0.52, to fix the rpi4 issue.
Though Gentoo does not seem to have its stabilized ebuild. Well.

[wernerb]

Thanks for the PR kinvolk/coreos-overlay#929.
From my understanding, we would have to also update dracut to >= 0.52, to fix the rpi4 issue.
Though Gentoo does not seem to have its stabilized ebuild. Well.

Yes, but not just for rpi4. Per my understanding all net/mdio modules are currently not working since kernel 5.10.

[t-lo]

To summarise, we would need to:

• merge Enable MDIO_BCM_UNIMAC for arm64 flatcar-archive/coreos-overlay#929
• update dracut to 053 (upstream gentoo ebuild available, even though it's masked currently [i.e. unstable])

Adding a label "good first issue" for users who want to accustom themselves with building custom images, assuming that both the kernel config change as well as the dracut version bump will be straightforward.

[dongsupark]

Fortunately Gentoo stablized dracut 053.
amd64: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=6a934a75bbc054b3ae7c14948df6a4ac6d69e643
arm64: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=a35bed081b36613d414a7a24534a4706e11fb2b0

[jepio]

The effect of the dracut fix still needs to be tested.

[raballew]

@jepio I used the latest version of the alpha channel on Raspberry Pi 4 and it seems that the issue is still present causing the same error as described in #227 (comment) when using iPXE to netboot. I will build a custom image later today and rerun the test.