Re: [Xen-devel] [PATCH RFC 00/19] arm64 EFI stub

[Roy Franz <roy.franz@xxxxxxxxxx>]

On Wed, Jul 2, 2014 at 5:31 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Wed, 2014-07-02 at 12:52 +0100, Ian Campbell wrote:
>> On Sat, 2014-06-28 at 02:25 +0100, Roy Franz wrote:
>> > 2) Is it valid to start XEN with a device tree that only contains
>> > multi-boot and EFI info? (As would be the case if the stub doesn't get a
>> > device tree as input.)
>>
>> This would be the case when running on an ACPI system I guess? In which
>> case everything which would be in the DT would instead be in the ACPI
>> tables, which is something Naresh is working on I think.
>>
>> >   Currently this isn't supported, some libfdt
>> > functions are missing, so I'm checking if this is desired before I add
>> > that.
>>
>> Unless this==booting with ACPI I'm not sure what it is and if its ACPI
>> I'm not sure what needs to be done in the stub, could you explain
>> please?
>>
>> (I have a feeling I'm missing something obvious)
>
> Ah, I think this is from the final patch:
>
>> +    if ( fdtfile->ptr )
>> +        fdt_size = fdt_totalsize(fdtfile->ptr);
>> +    else
>> +    {
>> +        /* RFRANZ_TODO - missing fdt_create_empty_tree() in libfdt. */
>> +        return NULL;
>> +    }
>
>
> I don't think we currently support booting with no FDT at all, and even
> in the ACPI world we would get one. So I think this would be an error.
> IOW no need to worry about it.
>

I think that for the ACPI-only case, the EFI stub will be the one
responsible for creating the FDT for passing the UEFI/ACPI to the XEN
kernel.  (I had overlooked the ACPI-only
case when considering the no-FDT case - for Linux we support this
since a kernel could be configured such that it needs nothing from the
FDT other than UEFI stuff, so we need to support it.)
So I think we will need this, but only for the ACPI-only case.  I'll
look at adding the required libfdt file that provides
fdt_create_empty_tree() - when I took a quick look it seemed that was
in a file by itself.  Matching the version of this new file with the
existing libfdt may add some complication, but I'll look into it.

Thanks,
Roy

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