Re: RFC: A new bootflow on ARM64 server using more of TF-A

Hi Arthur,

On 08.11.23 18:17, Arthur Heymans wrote:
> On ARM server platforms the 'preferred' way of informing the OS is via
> UEFI, ACPI and SMBIOS.
> There is some rationale on why:
> https://www.kernel.org/doc/Documentation/arm64/arm-acpi.txt
> TL;DR: "if you want to run an old kernel with new hardware ACPI could be a
> better solution than devicetree".

just a side note: For somebody working for a company that has used old
kernels on new hardware, this seems like a weak argument. I actually
remember more causes of trouble due to ACPI (and missing related changes
in the kernel). Chances that things really work multiplied by the
chances that somebody really needs such a setup seem pretty low. So
until I hear about some success stories, I'll consider it an empty
argument.

> Both the UEFI and ACPI spec are wild
> beasts to tame (with many pages) so ARM came up with essentially a TL;DR of
> that spec which is called Server Base Boot Requirements (
> https://documentation-service.arm.com/static/63cfe3aee4378a55c5e03d96?token=
> ).
>
> Now on a lot of existing ARM server platforms TF-A exists as 'full'
> solution. Currently the SBBR is satisfied by adding a EDK2 or other
> proprietary UEFI solution that gets loaded by TF-A. Not everyone likes
> these UEFI implementations as they are big and well... not so nice. So the
> idea came up to lighten that part of the burden (implementing tables and
> loading the OS):
> use coreboot to generate ACPI and SMBIOS (well supported on x86 and small
> changes needed for ARM), implement a small UEFI (e.g. with libpayload, just
> enough to load Linux from flash) to get a lightweight LinuxBoot firmware.

When I read below that TF-A hands off FDT, I thought this is
fascinating. Do you need any other input to generate ACPI and
SMBIOS? I have some idea in mind since FDT in coreboot was first
discussed during OSFC 2022: Clear coreboot from ACPI and produce
FDT instead. And for OSs that prefer ACPI, have a separate stage
that translates things. Didn't think about it, but with SMBIOS
it's quite the same. So eventually that would be something that
translates FDT --> ACPI, SMBIOS. Basically what you described
for ARM64.

Do you have any platform code / coreboot "port" published yet?
Could help to get an overview of what is needed :)

Cheers,
Nico

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