[Bug 2092205] Re: Using /etc/flash-kernel/machine in risc-v images does not permit building generic images

[Adriano Cordova Fedeli]

A fix won't be backported to Oracular as we will not be spinning new
images for it

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Title:
  Using /etc/flash-kernel/machine in risc-v images does not  permit
  building generic images

Status in livecd-rootfs package in Ubuntu:
  Fix Released
Status in livecd-rootfs source package in Noble:
  New

Bug description:
  In live-build/ubuntu-cpc/hooks.d/base/disk-image-uefi-non-cloud.binary we currently write file /etc/flash-kernel/machine to control which device-tree is copied to /boot and in subsequently to generate a devicetree command in grub.cfg.
  So
  We have only one image for the VisionFive 2 board but there are two revisions (1.2A, 1.3B) which require different device-trees.

  Instead of writing /etc/flash-kernel/machine, all device-trees of the
  current kernel could be copied to /boot/efi/dts/. U-Boot will then
  search this directory for a file called $filename and load it.
  Whenever the kernel will be updated, flash-kernel will copy the
  updated device-tree to /boot and GRUB will pick it up.

  [ Impact ]

  * This lets us build more generic images

  [ Test Plan ]

  * After creating RISC-V images with the proposed solution, the test
  plan is to verify that, on the first boot, all the device trees are
  located in /boot/dtbs, the kernel correctly exposes the machine from
  the firmware-provided device tree in /proc/device-tree, and grub.cfg
  does not yet include a devicetree entry. It is then necessary to
  ensure that kernel updates work correctly with the proposed solution;
  that is, after a kernel update, the script /etc/kernel/postinst.d/zz-
  flash-kernel creates the file /boot/dtb-$kernel_version, and this file
  is picked up by update-grub to create a devicetree entry for
  subsequent boots, pointing to /boot/dtb-$kernel_version.

  * Note that the first-boot behavior of this proposed model differs
  from the current working model: in the working model, the file
  /boot/dtb-$kernel_version is created together with the image, and on
  the first boot grub.cfg already contains a devicetree entry pointing
  to it. The kernel then uses this entry to populate /proc/device-tree,
  rather than using the firmware-provided device tree.

  [ Where problems could occur ]

  * Building of images might fail.
  * Usage of the correct device-trees after kernel upgrade might fail.

  [ Other Info ]

  n/a

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