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

[G Gregory]

On 2 February 2015 at 16:32, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> On Mon, Feb 02, 2015 at 01:50:52PM +0000, Graeme Gregory wrote:
>> On Mon, Feb 02, 2015 at 01:40:33PM +0000, Leif Lindholm wrote:
>> > On Mon, Feb 02, 2015 at 08:45:36PM +0800, Hanjun Guo wrote:
>> > > When system supporting both DT and ACPI but firmware providing
>> > > no dtb, we can use this linux,uefi-stub-generated-dtb property
>> > > to let kernel know that we can try ACPI configuration data even
>> > > if no "acpi=force" is passed in early parameters.
>> > >
>> > > CC: Mark Rutland <mark.rutland@xxxxxxx>
>> > > CC: Jonathan Corbet <corbet@xxxxxxx>
>> > > CC: Catalin Marinas <catalin.marinas@xxxxxxx>
>> > > CC: Will Deacon <will.deacon@xxxxxxx>
>> > > CC: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
>> > > CC: Grant Likely <grant.likely@xxxxxxxxxx>
>> > > CC: Matt Fleming <matt.fleming@xxxxxxxxx>
>> > > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
>> > > ---
>> > >  Documentation/arm/uefi.txt         |  3 +++
>> > >  arch/arm64/include/asm/acpi.h      |  1 +
>> > >  arch/arm64/kernel/setup.c          | 30 ++++++++++++++++++++++++++++++
>> > >  drivers/firmware/efi/libstub/fdt.c |  8 ++++++++
>> > >  4 files changed, 42 insertions(+)
>> > >
>> > > diff --git a/Documentation/arm/uefi.txt b/Documentation/arm/uefi.txt
>> > > index d60030a..5f86eae 100644
>> > > --- a/Documentation/arm/uefi.txt
>> > > +++ b/Documentation/arm/uefi.txt
>> > > @@ -60,5 +60,8 @@ linux,uefi-mmap-desc-ver  | 32-bit | Version of the mmap descriptor format.
>> > >  --------------------------------------------------------------------------------
>> > >  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.

Graeme
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