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Experimental Pi 5 image

Linux kernel packages

Until the Pi 5 is supported by Linux mainline and until suitable linux-image-* packages are available in Debian, it makes sense to ship a specific image for the Pi 5 that features linux-image-* packages (meta and regular) from Raspberry OS.

It makes little to no sense to ship the Debian packages as well, as they are not going to be useful, and might even make things complicated:

  • What happens when an update shows up in Debian? Could it be preferred over the Raspberry OS one for the following boot, effectively bricking the PiRogue running on Pi 5?
  • Additionally that means a slightly bigger image to download initially (~ 100 MB), plus useless upgrades later on.

If we decide to get rid of them, we must make sure we're not losing any other packages pulled via dependencies, or any kind of integration (e.g. initramfs hooks).

Firmware packages

A longstanding issue is that the raspi-firmware has been shipping Pi-related things from a very long while, mainly bootloader files and integration to make sure the Linux kernel image, the associated initramfs, and the DTBs are available under /boot/firmware. But that also include some wireless firmware files. It's been requested to move them to the existing firmware-brcm80211 package but that hasn't happened yet.

Unfortunately, Debian 12 doesn't ship firmware files making it possible to support the Pi 5 wireless interface (symptom: no wlan0 interface). That's why we're pulling firmware-brcm80211 from Raspberry OS in addition to Linux kernel packages. Since that package and Debian's raspi-firmware package have files in common, dpkg errors out when trying to install them side by side, that's why the Pi 5 image build uses --force-overwrite.

Open questions:

  • What happens if and when Debian ships an updated raspi-firmware package? Will that trigger a new file conflict? Gut feeling: yes. An update during Debian 12's lifetime (either via the security team or the release team) seems unlikely.
  • What happens if and when Raspberry OS ships an updated firmware-brcm80211 package? Will that trigger a new file conflict? Gut feeling: maybe not, if the initial overwrite triggered this package's being the registered owner of those files, we might be safe. An update during Debian 12's lifetime seems possible to probable, as the firmware-nonfree source package that builds this binary package might get updated to support newer hardware and/or to fix security and stability problems.

It would be good to test both cases to see what happens. If both break horribly and we want to be safe, we could adjust the APT pinning (pirogue.pref) to avoid upgrades for both packages, for example.