[SRU] flash-kernel to support xilinx kria platforms with noble kernel

[Talha Can Havadar]

[ Impact ]

 * With the current version of flash-kernel, users wont be able to boot into xilinx devices using optimised noble kernel because of the renaming of device-trees in kernel and cma configuration changes.

 * We need to fix this issue to keep support for xilinx devices in noble as well. This must not be back-ported into jammy since the kernel in jammy keeps the old names for device-trees and cma configuration in there didn't change

 * Patch will fix the issue by updating bootscript and `its` file to point correct device-tree files.

[ Test Plan ]

 * Flash the new image generated with new flash-kernel that has this fix
 * Try booting with new image
 * You should be able to reach the login prompt and be able to login using default username and password
 * This must work for all Kria devices listed below:
  - KV260
  - KR260
  - KD240

[ Where problems could occur ]
 * This change could only impact Xilinx Kria devices since it will only touch the files used by Xilinx Kria platforms including the ones listed above in test plan
 * Since this is an enablement patch for Ubuntu Noble image on Xilinx Kria platforms, there shouldnt be an impact to devices in the field.
 * If the patch is broken then the devices listed above will still continue to not work.

[ Other Info ]

 * This is based on changes in new optimised kernel: https://code.launchpad.net/~canonical-kernel/ubuntu/+source/linux-xilinx/+git/noble

[Loïc Minier (lool)]

Hi Talha,

This is subjective, but I would suggest not dropping the xilinx-zynqmp flavor from the list immediately for two reasons:
- might be useful across upgrades (e.g. I upgrade f-k but not the kernel)
- in the case of a backport of f-k

The f-k kernel flavors are an useful protection in the face of trying to run the raspi kernel on a xilinx platform, but I don't know if we'd gain much by enforcing the removal of the old kernel flavor name. We could drop it after the next LTS though.

[Loïc Minier (lool)]

Actually, sorry, I see that your other change on device tree names might require the new kernel flavor; are the new and old device tree names available in both old and new kernel? How do we ensure people don't upgrade to a broken combination?

[Loïc Minier (lool)]

For the CMA change, I guess it's easy enough to release note this in oracular, but I'm less clear on noble: are we going to reroll existing images with the change? How will we communicate on the differences between old and new images with larger and smaller CMA?

[Talha Can Havadar (tchavadar)]

Hi Loic,

new kernel doesnt have old device-trees at all. (this raises questions for the one upgrading from jammy, I feel like we need to create a transition package for linux-xilinx-zynqmp in noble so when people upgrade it it will install linux-xilinx)

But indeed for noble we should keep old kernel flavor as well. (so it will be like `Kernel-Flavors: xilinx xilinx-zynqmp`)

About the cma change, cma change will be documented in Xilinx Wiki.

[Loïc Minier (lool)]

I'm not sure if f-k supports having multiple device tree options; you probably also can't have multiple entries for the same machine but different kernels/device trees.

My recommendation would be to add both transitional packages for upgrades, and provide the old device tree name in the new kernel.

[Talha Can Havadar (tchavadar)]

kept the old kernel flavor for noble to make sure it is backwards compatible and attached new debdiff noble-2.debdiff

I will talk with kernel team about keeping the old device trees still in new kernel

[Loïc Minier (lool)]

Alternatively, you can add a versioned conflict on f-k in the kernel package (Breaks << versions of f-k prior to the change)

[Talha Can Havadar (tchavadar)]

I think breaks is better in this case makes kernel clean