Re: [PATCH v3 1/5] efi_loader: bootmgr: preserve a passed devicetree

[Carlo Caione <ccaione@baylibre.com>]

On Mon, Sep 28, 2026 at 15:00:03 +0100, E Shattow wrote:
 
> I understand the need for what you describe, however the method of doing
> this is also not clear for me.
> 
> When I have encountered this situation the workaround was to invalidate
> the 'model' compatible property in the tree to prevent a later match and
> whatever process from installing a different Fdt than what I wrote on
> the 'bootefi' command invocation in U-Boot.
> 
> An example of this is the Debian Linux 'mini.efi' netinst
> debian-installer on riscv64 architecture. The 'mini.efi' contains dtb
> information for multiple targets, and there is not much configuration
> choice about this. It would be useful to suppress the Fdt passing logic
> that occurs through EFI, to mask any of the model compatible (possible
> using u-boot 'fdt' command), Fdt, and fdtfile name.
> 
> I would like to see actual examples of why this series is needed.

Hi E,

The case I want to support with this work is booting an unmodified
generic EFI distribution from SD while supplying the board DT and
overlays from firmware storage on eMMC (this is a very specific use-case
but you get the gist).

The FIT describes the supported combinations and, with required
configuration signatures, authenticates the selected combination
independently of the OS image.

About the mini.efi objection, I think that is the same distinction
previously discussed with Simon for GRUB (see [0]): this series controls
the DT U-Boot initially supplies, but cannot prevent an EFI application
from subsequently replacing it.

Basically Patch 1 addresses replacement inside U-Boot, before the EFI
application starts but it does not force subsequent EFI software to
retain it.

Let me know your thought about this,

cheers!

[0] https://lore.kernel.org/all/CADh8LscEUi5kvGQ28GErjEM=WvQ=6t0p5Kh30jQ-S8ZapG8yrw@mail.gmail.com/

--
Carlo Caione