[PATCH] arm: init: add an option to use FDT from previous bootloader

[Simon Glass]

Hi Caleb,

On Tue, 24 Oct 2023 at 11:10, Caleb Connolly <caleb.connolly at linaro.org> wrote:
>
>
>
> On 24/10/2023 19:03, Simon Glass wrote:
> > Hi Caleb,
> >
> > On Tue, 24 Oct 2023 at 04:32, Caleb Connolly <caleb.connolly at linaro.org> wrote:
> >>
> >> Add a new config option to allow u-boot to reuse the FDT provided by the
> >
> > U-Boot (please fix throughout)
>
> Will do!
> >
> >> previous stage bootloader when available.
> >>
> >> On some boards the previous stage bootloader can populate
> >> platform-specific parts of the devicetree such as the memory node, this
> >> allows us to avoid hardcoding it in u-boot and instead determine it
> >> dynamically at runtime.
> >>
> >> Signed-off-by: Caleb Connolly <caleb.connolly at linaro.org>
> >> ---
> >> This patch will improve generic support for Qualcomm boards by enabling
> >> us to configure the memory map at runtime rather than having hardcoded
> >> maps on a per-device basis. I've gone for this approach initially to try
> >> and avoid introducing board specific code where possible, but I'm happy
> >> to rework this into mach-snapdragon if that's preferred.
> >
> > Do you think it could use bloblist instead? I did send a patch to use
> > the FDT in the bloblist:
>
> If it would require changes to the previous stage bootloader then
> unfortunately not. We're mostly stuck with the behaviour that we've got
> for now...

Yes it would. What is the previous-stage bootloader?

>
> This mechanism of retrieving the DTB is also used on the apple M1 I
> think, and any other board where we're booting U-Boot as a drop-in for
> the kernel on arm64.

I believe M1 is an open source project so perhaps they could adopt
firmware handoff when it is finalised.

Anyway, can this use OF_BOARD instead, perhaps? It already permits
board-specific actions and is used by some rpi boards.

> >
> > https://patchwork.ozlabs.org/project/uboot/patch/20230926141514.2101787-40-sjg@chromium.org/
> >
> > Regards,
> > Simon
> >

Regards,
Simon