Re: [PATCH v8 08/21] dt / chosen: Add linux,uefi-stub-generated-dtb property

[Hanjun Guo]

On 2015å02æ07æ 13:03, Ard Biesheuvel wrote:
> On 7 February 2015 at 03:36, Hanjun Guo <hanjun.guo@xxxxxxxxxx> wrote:
> > On 2015å02æ06æ 18:34, G Gregory wrote:
> > [...]
> >
> > > > > > > --------------------------------------------------------------------------------
> > > > > > >    linux,uefi-stub-kern-ver  | string | Copy of linux_banner from
> > > > > > > build.
> > > > > > >
> > > > > > > --------------------------------------------------------------------------------
> > > > > > > +linux,uefi-stub-generated-dtb  | bool | Indication for no DTB
> > > > > > > provided by
> > > > > > > +                        |      | firmware.
> > > > > > >
> > > > > > > +--------------------------------------------------------------------------------
> > > > > >
> > > > > >
> > > > > > Apologies for the late bikeshedding, but the discussion on this topic
> > > > > > previsously was lively enough that I thought I'd let it die down a bit
> > > > > > before seeing if I had anything to add.
> > > > > >
> > > > > > That, and I just realised something:
> > > > > > One alternative to this added DT entry is that we could treat the
> > > > > > absence of a registered UEFI configuration table as the indication
> > > > > > that no HW description was provided from firmware, since the stub does
> > > > > > not call InstallConfigurationTable() on the DT it generates. This does
> > > > > > move the ability to detect to after efi_init(), but this should be
> > > > > > fine for ACPI-purposes.
> > > > > That would not work as expected in the kexec/Xen use case though as they
> > > > > may genuinely boot with DT from an ACPI host without UEFI.
> > > >
> > > >
> > > > I'm a little concerned by this case. How do we intend to pass stuff from
> > > > Xen to the kernel in this case? When we initially discussed the stub
> > > > prior to merging, we weren't quite sure if ACPI without UEFI was
> > > > entirely safe.
> > > >
> > > > The linux,uefi-stub-kern-ver property was originally intended as a
> > > > sanity-check feature to ensure nothing (including Xen) masqueraded as
> > > > the stub, but for some reason the actual sanity check was never
> > > > implemented.
> > > >
> > > > > > If that is deemed undesirable, I would still prefer Catalin's
> > > > > > suggested name ("linux,bare-dtb"), which describes the state rather
> > > > > > than the route we took to get there.
> > > > > I agree.
> > > >
> > > >
> > > > I guess this would be ok, though it would be nice to know which agent
> > > > generated the DTB.
> > >
> > > The most obvious scheme then is
> > >
> > > linux,bare-dtb = "uefi-stub";
> > >
> > > otherwise we generate a new binding for every component in the boot path.
> >
> >
> > Leif, Mark, any comments on this?
>
> As far as I remember, we did not finalize the decision to go with a
> stub generated property instead of some other means to infer that the
> device tree is not suitable for booting and ACPI should be preferred.
>
> We will be discussing the 'stub<->kernel interface as a boot protocol'
> topic this week at Connect, so let's discuss it in that context before
> signing off on patches like these.

OK, see you guys in Hongkong.

Thanks
Hanjun
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