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

[Adam Smith]

The current thinking seems to be that efi passes grub2 the flattened
device tree.  The problem with this is that the dtb is not at all
stable.  It is supposed to be independent of operating system, but there
are differences between the upstream and rpi foundation kernels.  Grub2
or U-boot can give the user the choice of kernel or even operating
system, but it could be fed an incompatible dtb by efi.  Grub2 can load
a device tree which solves this, but you currently loose the overlays.

Having said all of that, the dtb is stable enough not to require always
updating on every kernel update.  This is how flash-kernel can get away
with not updating the overlays.  But the safest thing is not to update
the dtb, so that the overlays are in-sync.  Kernel drivers are supposed
to (if they are written correctly) be able to cope with an old dtb file.

I suggest that Linux-firmware-raspi2 handles updating the dtb files, and
it does so infrequently and only when necessary.

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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:
  New

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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