Ethernet on the BananaPi M2 Zero

Even though it does not look like it does, the BPI-M2 Zero also has a wired ethernet interface. Unfortunately, it is disabled by default in its device tree blob.

But enabling it is easy:

# copy into /root
cp /boot/dtb/sun8i-h2-plus-bananapi-m2-zero.dtb .
# decompile
dtc -I dtb sun8i-h2-plus-bananapi-m2-zero.dtb \
    -O dts -o sun8i-h2-plus-bananapi-m2-zero.dts
# edit
vi sun8i-h2-plus-bananapi-m2-zero.dts # :-)
# compile
dtc -i dts sun8i-h2-plus-bananapi-m2-zero.dts \
    -O dtb -o /boot/custom.dtb

How do you need to edit the DTB file?

In the "ethernet@1c30000" block, you need to apply this "diff":

-       status = "disabled";
+       status = "okay";
+       phy-handle = <0x4d>;
+       phy-mode = "mii";
        phandle = <0x4b>;

The "phy-handle" value is taken from the "phandle" of the "ethernet-phy@1" block a few lines down. Then another change is adding an alias for ethernet0 to the "aliases" block:

       aliases { 

              serial0 = "/soc/serial@1c28000";
              serial1 = "/soc/serial@1c28400";
+             ethernet0 = "/soc/ethernet@1c30000";
       };

Ethernet will work without that, but we'll need this for setting the MAC address later.

Now reboot and try it out in a temporary way. Either by:

• interrupting u-boot and doing setenv fdtfile custom.dtb (no "saveenv" yet!), then "boot"
• editing the GRUB menu, adding an additional line after "initrd..." that reads devicetree /boot/custom.dtb

Check if the ethernet device eth0 appears after boot. If it does, the u-boot method can be persisted by issuing a saveenv command after the setenv.

Persisting the MAC address:

At my first tries I noticed that the MAC address was randomly assigned on every boot, in later experiments I could not reproduce this anymore but it looked like the MAC was at least reassigned on every deployment. I have no idea if this has to do with saving the environment in u-boot or if there is something in the userspace (a systemd service maybe?) that makes the MAC address semi-persistent. I decided to fix the MAC address once and for all, since I'm running a static DHCP setup, this is pretty important for my use case.

Because of the "ethernet0" alias in the device tree, persisting the MAC address is easy. All you need to do is setenv ethaddr 22:33:44:55:66:77 in u-boot and then persist this with saveenv and you are done. Note that u-boot has some precautions to disallow changing the MAC address later by accident so you are not able to easily undo this later. You can always remove "/boot/efi/uboot.env" in your booted system or by inserting the SD card into another machine and start from scratch.

GRUB, u-boot, kernels and DTB loading (on the BPi M2 Zero and others)

While I was experimenting with the BananaPi M2 Zero board, I soon needed to adopt its device tree file (dtb).

Fortunately, the friendly members of the openSUSE:Factory:ARM community quickly hinted me at the grub2 "devicetree" command which can be specified similar to "linux" or "initrd" to name a file that's loaded as device tree.

Unfortunately, there is no way to make this really persistent, short of editing the grub generator scripts which will get lost on every grub2 update.

The other option would be to decompile the board's DTB file ("/boot/dtb/sun8i-h2-plus-bananapi-m2-zero.dtb" in my case), change and then recompile it, replacing the original file. This has two downsides: first, it will get overwritten with every update of the "dtb-sun8i" package (no idea how often this will be the case) and second, you might want to have the original file as fallback ready. In general, editing package managed files is not a good idea in my book, if it can be avoided it should be.

So I looked into the "who loads which device tree file" and found out that actually the dtb is loaded by u-boot, even before grub starts. U-boot has the name of the board built-in and thus the file name it is looking for. Additionally it has a search list of directories that it searches to find the dtb file. So the simplest way to apply your own dtb file would probably be to put it, with the original file name into the search path after the original file. I tried this approach at first, but then went for explicitly specifying a different filename, which is just not as subtle in case you need to debug this years later ;-)

So the method is relatively easy:

1. put your modified dtb file into /boot, I named it custom.dtb.
2. boot into u-boot, interrupt booting on the serial console
3. in u-boot console, enter setenv fdtfile custom.dtb
4. in u-boot console, enter saveenv

That's it. Now boot and verify that your dtb file is used.

Note that the u-boot environment is saved on the EFI partition of the SD card (first partition, FAT format) as file "uboot.env". If you need to reset the environment to the built-in defaults, then you can always mount the SD card in another machine and move away or delete uboot.env.

openSUSE Tumbleweed on the Banana Pi BPI-M2 ZERO

This is the first post of a small series about openSUSE on the Banana Pi BPI-M2 ZERO.

Preface

I recently got myself a Banana Pi M2 Zero board while ordering other stuff at an electronics distributor. The M2 zero is the same form factor and feature set as the Raspberry Pi Zero W (the GPIO pin headers are said to be compatible, it has WiFi and Bluetooth built in and an USB OTG port). The CPU is an Allwinner H2+, a quad-core ARM processor running a 1GHz clock speed, RAM size is 512MB. Processing power is probably comparable to a Raspberry Pi 2 board.

I bought the M2 Zero to use it with an RTLSDR stick to receive the signal of my outside RF temperature sensor. This worked with the Raspberry Pi Zero W, but was a bit too much for the slower CPU which has other more important things to do anyway (playing internet radio ;-), so the M2 Zero was a cheap, more powerful alternative. The box will be running headless and thus I do not care about support for graphics and multimedia anyway.

In the end, I switched the RF receiver to a RaspyRFM board whih is using less energy and simpler to use than an RTLSDR stick just to receive some sensors and now the M2 Zero board is free for tinkering...

openSUSE on the M2 Zero

There was already an image available for the Banana Pi M2 Plus (called "sinovoipbpim2plus"), which is the "bigger brother" of the M2 zero, but that image did not boot. Experimenting with the u-boot image from armbian lead to success in "openSUSE Tumbleweed boots with armbian u-boot". Thanks to the friendly openSUSE ARM community, a matching u-boot version for the M2 Zero was built quickly and I could submit the updated image in OBS to get an image ready for the board (called "sinovoipbpim2zero").

Some small things are still to be sorted out, this is why I would suggest you use the image from the home:seife:bananapi repository for now. Since the board has only WiFi networking (more on that in a later post...), you'll need a serial console wired up for initial setup and I strongly suggest to use at least the "openSUSE-Tumbleweed-ARM-X11-..." image and not the JeOS image, since JeOS does not contain NetworkManager and using WiFi with wicked (actually using anything with wicked) is not fun.

So put the image on the SD card, connect the serial console, boot the box up. Log in as root. WiFi connection is easily established then:

nmcli dev wifi connect YOUR_SSID password YOUR_PASSWORD

That's it, have fun! ;-)

Addon note: When I started to write this post, my home:seife:bananapi repo was necessary for actually getting WiFi to work (contained a fixed kernel-firmware package). This has all been submitted to upstream or openSUSE:Factory:ARM now. All that's "special" in my repo now is a slightly extended package selection in the image (the "dtc" package is included) and a fixed config.sh script that makes NetworkManager actually work correctly, including name resolution, see boo#1180234 for details), so the image from openSUSE:Factory:ARM should be "good enough" for most uses already and in the near future I'll probably retire the home:seife:bananapi project or use it just for development stuff).