[Bug 1765628] Re: Create an image for all raspberry models

[Dave Jones]

Going back through old bugs - I think we can mark this "Fix Released" at
this point; the classic and core images are now unified (while the
+raspi2, +raspi3, +cm3 images *appear* to exist in some cases these are
now just links to the unified image).

Just to address a couple of the other comments above:

* I updated flash-kernel last year to add a special-cased "pi" method
that now copies *all* discovered DTBs (and overlays) when it runs,
permitting an SD card to be moved between support Pis (this was
necessary for the upgrade story on Bionic to support the Pi4 on existing
installations).

* u-boot is a bit of a pain on the images but we do use it for two
relatively important things:

* on Core it's used to support the A/B boot procedure. This requires a
bootloader with writeable state (the Pi's built-in bootloader is
deliberately read-only for simplicity and safety, but this means it
cannot support an A/B boot case).

* on Classic (and Core in future) it's used to support decompressing the
arm64 kernel which doesn't support self-extracting compression.

So, for the time being at least, u-boot and flash-kernel are likely to
stay. As far as future designs are concerned, I don't particularly like
the EFI option as it means adding yet *another* component into our boot
process (alongside u-boot). I'd much rather move the opposite way and
remove a component (u-boot), just relying on the pi's bootloader.
However, that would require the pi's bootloader to grow features
covering the two cases above (which isn't out of the question, but I've
no idea if/when that may happen).

As for flash-kernel - I don't see that going away at the moment (for the
reasons ogra's mentioned above), and with the "pi" special case in there
I'm reasonably happy with it staying.

** Changed in: livecd-rootfs (Ubuntu)
       Status: Confirmed => Fix Released

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https://bugs.launchpad.net/bugs/1765628

Title:
  Create an image for all raspberry models

Status in livecd-rootfs package in Ubuntu:
  Fix Released

Bug description:
  Currently (Xenial to Bionic) server images only run on the raspberry
  pi 2.  This is due to the u-boot bootloader.

  However it is possible to produce one image that runs on a pi 2 and 3.
  Fedora arm 32 bit produce such an image.  They make use of conditional
  filters in the config.txt
  (https://www.raspberrypi.org/documentation/configuration/config-
  txt/conditional.md ) and put two versions of u-boot on the image.

  They other way to do it is to remove u-boot entirely and just rely on
  the internal pi bootloader to sort it out.  This could be permanent,
  or just for first boot where upon flash-installer is called to install
  the correct u-boot file.

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