[PATCH v2 1/1] efi_loader: architecture specific UEFI setup

[Atish Patra]

On Thu, Feb 6, 2020 at 12:10 PM Alexander Graf <agraf at csgraf.de> wrote:
>
>
> On 06.02.20 19:28, Atish Patra wrote:
> > On Tue, Feb 4, 2020 at 11:43 PM Ard Biesheuvel
> > <ard.biesheuvel at linaro.org> wrote:
> >> On Wed, 5 Feb 2020 at 05:53, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >>> RISC-V booting currently is based on a per boot stage lottery to determine
> >>> the active CPU. The Hart State Management (HSM) SBI extension replaces
> >>> this lottery by using a dedicated primary CPU.
> >>>
> >>> Cf. Hart State Management Extension, Extension ID: 0x48534D (HSM)
> >>> https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.adoc
> >>>
> >>> In this scenario the id of the active hart has to be passed from boot stage
> >>> to boot stage. Using a UEFI variable would provide an easy implementation.
> >>>
> >>> This patch provides a weak function that is called at the end of the setup
> >>> of U-Boot's UEFI sub-system. By overriding this function architecture
> >>> specific UEFI variables or configuration tables can be created.
> >>>
> >>> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> >>> Reviewed-by: Atish Patra <atish.patra at wdc.com>
> >> OK, so I have a couple of questions:
> >>
> >> - does RISC-V use device tree? if so, why are you not passing the
> >> active hart via a property in the /chosen node?
> > Yes. RISC-V uses device tree. Technically, we can pass the active hart
> > by a DT property
> > but that means we have to modify the DT in OpenSBI (RISC-V specific
> > run time service provider).
> > We have been trying to avoid that if possible so that DT is not
> > bounced around. This also limits
> > U-Boot to have its own device tree.
>
>
> I don't understand how this is different from the UEFI variable scheme
> proposed here? If you want to create an SBI interface to propagate the
> active HART that U-Boot then uses to populate the /chosen property,
> that's probably fine as well.
>

We don't want to create SBI interface to pass this information.

> We already have hooks that allow you to modify the DT right before it
> gets delivered to the payload. Just add it there?
>

Hmm. I guess it is true if the DT is loaded from MMC or network as well.
How about EDK2 ? If we go DT route, it also has to modify the DT to
pass the boot hart.

As it requires DT modification in multiple projects, why not use efi
configuration tables as
suggested by Ard ?

> >
> >
> >> I'd assume the EFI stub would not care at all about this information, and it would give
> >> you a Linux/RISC-V specific way to convey this information that is
> >> independent of EFI.
> > Yes. EFI stub doesn't care about this information. However, it needs
> > to save the information somewhere
> > so that it can pass to the real kernel after exiting boot time services.
>
>
> DT sounds like a pretty natural choice for that to me :).
>
>
> Alex
>
>


-- 
Regards,
Atish