Re: [Xen-devel] [PATCH 15/15] xen: tools: expose EPC in ACPI table

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Jul 18, 2017 at 08:36:15PM +1200, Huang, Kai wrote:
> 
> 
> On 7/17/2017 10:54 PM, Roger Pau Monné wrote:
> > On Sun, Jul 09, 2017 at 08:16:05PM +1200, Kai Huang wrote:
> > > On physical machine EPC is exposed in ACPI table via "INT0E0C". Although 
> > > EPC
> > > can be discovered by CPUID but Windows driver requires EPC to be exposed 
> > > in
> > > ACPI table as well. This patch exposes EPC in ACPI table.
> > > 
> > > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxxxxxxxx>
> > > ---
> > >   tools/firmware/hvmloader/util.c  | 23 +++++++++++++++++++
> > >   tools/firmware/hvmloader/util.h  |  3 +++
> > 
> > Is there any reason this needs to be done in hvmloader instead of
> > libacpi? I'm mostly asking this because PVH guests can also get ACPI
> > tables, so it would be good to be able to expose EPC to them using
> > ACPI.
> 
> Hi Roger,
> 
> Thanks for comments. I didn't deliberately choose to do in hvmloader instead
> of libacpi. It seems libxl only builds ACPI table when guest is HVM, and it
> doesn't use any device model, and I think I have covered this part (see
> changes to init_acpi_config). Is there anything that I missed?

dsdt.asl is only used for HVM guests, PVH guests basically get an
empty dsdt + dsdt_acpi_info + processor objects populated by make_dsdt
(see Makefile in libacpi), so they end up without the EPC Device
block.

It would be good if a new empty dsdt is created, that contains the
Device EPC block, or a ssdt is used, and it's added to both HVM/PVH
guests.

Alternatively you could also code the EPC Device block in mk_dsdt, but
that's going to be cumbersome IMHO.

Thanks, Roger.

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