Re: [Xen-devel] [RFC] ARM VM System Sepcification

[Christoffer Dall <christoffer.dall@xxxxxxxxxx>]

On Thu, Feb 27, 2014 at 10:05:05AM +1300, Michael Hudson-Doyle wrote:
> Christoffer Dall <christoffer.dall@xxxxxxxxxx> writes:
> 
> > Hardware Description
> > --------------------
> > The Linux kernel's proper entry point always takes a pointer to an FDT,
> > regardless of the boot mechanism, firmware, and hardware description
> > method.  Even on real hardware which only supports ACPI and UEFI, the kernel
> > entry point will still receive a pointer to a simple FDT, generated by
> > the Linux kernel UEFI stub, containing a pointer to the UEFI system
> > table.  The kernel can then discover ACPI from the system tables.  The
> > presence of ACPI vs. FDT is therefore always itself discoverable,
> > through the FDT.
> >
> > Therefore, the VM implementation must provide through its UEFI
> > implementation, either:
> >
> >   a complete FDT which describes the entire VM system and will boot
> >   mainline kernels driven by device tree alone, or
> >
> >   no FDT.  In this case, the VM implementation must provide ACPI, and
> >   the OS must be able to locate the ACPI root pointer through the UEFI
> >   system table.
> 
> Maybe I'm missing something, but should this last bit say "a trivial
> FDT" instead of "no FDT"?  If not, I don't understand the first
> paragraph :-)
> 
That trivial FDT would be generated by the EFI stub in the kernel - not
provided by the VM implementation.

-Christoffer

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