I know it’s a cross-post, but since this is not on the cheap, but rather on the libre side: Have you checked out the MNT Pocket Reform?

I haven’t looked at the schematics, so I am not certain which connection exactly would be needed. I only know that the Reform Mainboard and the Reform CM4 adapter don’t expose any way of writing to the eMMC other than booting the system first. The problem here is that the Banana Pi CM4 boot process first looks for a bootloader in eMMC, and only if it cannot find one there, tries the SD card. So, if one flashes a bootloader that gets recognized by the firmware, but that later fails to boot, one is stuck…

The I/O board on the other hand allows to connect to the CM4 via USB, and there is a weird, but supposedly working, procedure to erase the data in eMMC.

In any case, I now have a spare CM4 I/O board lying around, and if I ever choose to upgrade my Reform to the Rockchip SoM (or something even faster), I can then still use the CM4 as a small standalone PC.

At least in my case, the default OS came on an SD Card, and both, the M.2 SSD (which I had ordered together with the laptop) and the eMMC were empty. The manual contains a section about moving the OS to eMMC, so I guess that’s their default setup.

(In my case there’s an additional thing though: For the Banana Pi CM4 SoM the installation of u-boot into eMMC is officially not supported, as one would need a CM4 I/O board to erase it again, if anything goes wrong. I installed it there anyhow, and it’s working for me, but I did buy the I/O board beforehand as a precaution.)

I am curious how much work it will be to modify that Ubuntu image to fully work on the Reform. The audio chip and some other peripherals are on the mainboard, and need to be included in the device tree for the kernel to pick them up, so I would expect that at least some modifications of the image are needed.

It might already be enough to grab the device tree from the MNT gitlab, compile it, and put it in the boot partition for stuff to work. (You will likely also want to install the reform-tools - either from their gitlab or from their repository. They include a kernel module that is needed to get battery readout and to power off the laptop on shutdown.)

What helped me a lot while setting up the system was that I kept the SD card with the official (Debian Unstable) image around - every time something didn’t work, I could boot it up and check how the official image does it.

I own one, and am really happy with it. There is some jank to expect though:

• The official system image is based on Debian Unstable. This means that you frequently get broken updates (for instance, currently waybar is broken, and just a few days ago, boot got broken by a buggy initramfs).
  • At least for some SoMs there are also Debian Stable images available, which are, well, stable.
  • I am running Gentoo on my Reform, and once one gets past the initial setup (kernel config is a challenge) it works pretty well. I have written a blog post about installing Gentoo on the Reform.
• DPMS off might not work reliably (depending on SoM). I got it working well on my BananaPi CM4 SoM by changing sway config though.
• Suspend-to-disk (hibernate) does currently not work. Last time I tried it, the system continued just fine, but froze a few seconds later.
  • No clue if standby works. I don’t use standby.
• Some other issues exist with the Banana Pi CM4, but there are workarounds: https://community.mnt.re/t/tracking-known-issues-and-solutions-with-the-bpi-a311d-upgrade
• There are probably more issues that I cannot remember right now.

That said: Now that I have Gentoo running on it, and found workarounds for the most annoying issues (except for the suspend-to-disk issue), I am loving the laptop and would not trade it for anything else.