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Re: [PATCH 0/4] xen/arm: Unbreak ACPI

On Tue, Oct 13, 2020 at 06:06:26PM -0700, Stefano Stabellini wrote:
> On Mon, 12 Oct 2020, Elliott Mitchell wrote:
> > I'm on different hardware, but some folks have setup Tianocore for it.
> > According to Documentation/arm64/acpi_object_usage.rst,
> > "Required: DSDT, FADT, GTDT, MADT, MCFG, RSDP, SPCR, XSDT".  Yet when
> > booting a Linux kernel directly on the hardware it lists APIC, BGRT,
> > 
> > I don't know whether Linux's ACPI code omits mention of some required
> > tables and merely panics if they're absent.  Yet I'm speculating the list
> > of required tables has shrunk, SPCR is no longer required, and the
> > documentation is out of date.  Perhaps SPCR was required in early Linux
> > ACPI implementations, but more recent ones removed that requirement?
> I have just checked and SPCR is still a mandatory table in the latest
> SBBR specification. It is probably one of those cases where the firmware
> claims to be SBBR compliant, but it is not, and it happens to work with
> Linux.

Is meeting the SBBR specification supposed to be a requirement of running

I don't seen any mention of such.
`find docs xen/arch/arm -type f -print0 | xargs -0 grep -eSBBR` produces
no output.

Perhaps you've been adding this as a presumptive requirement since
previously the only hardware capable of running Xen due to an
appropriately unlocked bootloader was SBBR compliant?  If so, it seems
time to either add this as an explicit requirement and document it, or
else remove this implicit requirement and start acting as such.

The Raspberry PI 4B has a UEFI implementation available which is based on
Tianocore.  No statement has been made of it qualifying as SBBR.  Yet it
is clearly mostly able to boot Xen, just this is exposing issues.

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