Re: [PATCH 11/12] efi/loongarch: libstub: remove dependency on flattened DT

[Ard Biesheuvel <ardb@kernel.org>]

On Mon, 19 Sept 2022 at 08:06, Huacai Chen <chenhuacai@kernel.org> wrote:
>
>  Hi, Ard,
>
> On Mon, Sep 19, 2022 at 1:15 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Mon, 19 Sept 2022 at 03:58, Huacai Chen <chenhuacai@kernel.org> wrote:
> > >
> > > Hi, Ard,
> > >
> > > I think the parameters passed to the core kernel need to be discussed.
> > > The old way (so-called old world):
> > > a0=argc, a1=argv, a1=bpi
> > >
> > > The current way (so-called new world):
> > > a0=efi boot flag, a1=fdt pointer
> > >
> > > The new way (in this patchset):
> > > a0=efi boot flag, a1=systemtable, a2=cmdline
> > >
> > > I prefer to use the current way, there are 3 reasons:
> > > 1, both acpi system and dt system can use the same parameters passing method;
> >
> > DT systems will use this too. The distinction is between EFI boot and
> > non-EFI boot. We *really* should keep these separate, given the
> > experience on ARM, where other projects invent ways to pass those
> > values to the kernel without going through the stub.
> In the last patch I see:
> +               void *fdt_ptr = early_memremap_ro(fw_arg1, SZ_64K);
> +
> +               early_init_dt_scan(fdt_ptr);
> +               early_init_fdt_reserve_self();
> +
>                 clear_bit(EFI_BOOT, &efi.flags);
> So I suppose for the DT system that means a0=efi boot flag, a1=fdt
> pointer, a2=cmdline? Then it is not exactly the same as the ACPI
> system, but similar.
>

No, for non-EFI DT boot, the command line is passed via the DT, so
a0=0x0 (non-efi), a1=DT, a2=0x0

Do you intend to support non-EFI DT boot by the way?

So

a2  != 0x0 means old world
a0 != 0x0 means EFI boot, a1 is the command line
a0 == 0x0 means !EFI boot, a1 is the DT

> >
> > > 2, arm64, riscv and loongarch can use similar logics (light FDT);
> >
> > No need to repeat a mistake. I intend to fix RISC-V next.
> >
> > > 3, out-of-tree patches can make compatibility with the old world
> > > easier by just judging whether a2 is zero.
> > >
> >
> > The whole point of this series is that the EFI stub should not be
> > touching the DT at all. In other words, there is no DT pointer, so the
> > current method needs to be revised.
> >
> > What we might do is
> >
> > a0=systemtable, a1=cmdline
> >
> > as any non-zero value is treated as logic true. That way, your logic
> > to test a2 is zero will still work.
> I think the efi boot flag is still needed, even boot from efistub.
> Because if boot with "efi=novamap", the efi runtime should be
> disabled. Then we need efi_enabled(EFI_BOOT) to be false in
> efi_init().
>

I don't think it makes sense to allow efi=novamap on LoongArch, given
that we cannot make use of the runtime services that way. So in my
code, efi_novamap is set to false unconditionally.