Problems compiling/loading out of tree kernel modules

Product support balenaOS
1

Hi there,

I am trying to compile Realtek RTL8822bu and ath10k kernel modules of various wireless cards for RaspberryPi Computing Module 3+. I had done it last year and it worked, but it fails with recent kernels (with rebuilds of course). We use various mini PCIe cards if that matters (such as WPEQ-257ACN - QCA9882 2T2R AP-Mode Module | SparkLAN and WPET-236ACN(BT) - RTL8822BU 2T2R USB Module | SparkLAN which use Realtek and ath10k respectively). FWIW at least ath10k is already in the mainline kernel which is surprisingly missing from balena OS.

I am aware of GitHub - balena-os/kernel-module-build: Example project for building an OOT kernel module in balena. Initially I used that to compile GitHub - jeremyb31/rtl8822bu: RTL8822BU Wireless Driver for Linux. I have tried rebuilding for kernels 2.75.0+rev1 and 2.72.0+rev both production and development images. They build fine but produce segfaults upon insmoding in a container ( I try modprobing the dependencies such as cfg80211 first). Please see the attached text file for kernel ring logs upon insmod.
segfault.txt (76.7 KB)

I have tried compiling with the example project mentioned above and also with the make instructions from the wireguard example which is much simpler and straightforward (GitHub - klutchell/balena-wireguard: wireguard stack for balenacloud). I also tried cross-compiling the kernel module locally using the kernel-headers from the balena S3 (such as in the wireguard example, or by looking at the build.sh file and figuring it out). No matter what, I get the segfault on the same device which used to work.

Here are our two big pain points:

1- How to get rid of segfaults and make this work?
2- How to compile other drivers which support AP mode.

For AP mode I need to compile another driver such as GitHub - morrownr/88x2bu: Linux Driver for USB WiFi Adapters that are based on the RTL8812BU and RTL8822BU Chipsets or GitHub - cilynx/rtl88x2bu: rtl88x2bu driver updated for current kernels.. They don’t even compile with balena. The second one uses dkms and works perfectly fine on a debian, but I was unable to use dkms with balena example project.

I’d appreciate your support for solving these problems which could benefit anyone trying to get wireless support.

Edit:
It would be also very helpful to provide customers with a template that allows easy compilation of in-kernel modules which are missing from balenaOS versions (such as ath10k). That will make working with balena more productive and increases adaption.

4

Hi, we are aware that building in-tree and out-of-tree kernel modules is one of the pain points of the platform and we are working towards a much smoother process.

If you require a specific in-tree networking driver we can include it as part of the standard BalenaOS release.

For the out-of-tree kernel modules, do you have the drivers building and working with a different distribution that also runs a 5.4 based kernel? You mention they work fine on Debian, what kernel version is this Debian version running?