Re: [Qemu-devel] [PATCH] acpi: switch to a dummy SSDT

[Stefan Berger]

On 01/10/2018 06:29 AM, Michael S. Tsirkin wrote:
> On Wed, Jan 10, 2018 at 12:25:34PM +0100, Igor Mammedov wrote:
> > On Tue, 9 Jan 2018 15:58:11 +0200
> > "Michael S. Tsirkin" <address@hidden> wrote:
> >
> > > We prefer not changing table sizes depending on parameters,
> > > that's why we create a dummy table rather than just drop
> > > the MCFG table.
> > >
> > > However, a table named "QEMU" could be put to a better
> > > use than just a stub, e.g. we could use it to pass
> > > some QEMU specific info to guests.
> > >
> > > Replace with an SSDT and pad with the Nop opcode
> > > to preserve the length.
> > Not sure it's useful, do you have patches on top of that, which will use this?
> Yes but not me - Stefan (Cc'd) wants to add a custom table.

With the virtual device at a well known address I don't need the custom 
table anymore...

   Stefan
> > > Signed-off-by: Michael S. Tsirkin <address@hidden>
> > > ---
> > >   hw/i386/acpi-build.c | 17 ++++++++++++-----
> > >   1 file changed, 12 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > > index 73519ab..d0afb31e 100644
> > > --- a/hw/i386/acpi-build.c
> > > +++ b/hw/i386/acpi-build.c
> > > @@ -2419,6 +2419,8 @@ build_mcfg_q35(GArray *table_data, BIOSLinker *linker, 
> > > AcpiMcfgInfo *info)
> > >   {
> > >       AcpiTableMcfg *mcfg;
> > >       const char *sig;
> > > +    const char *oem;
> > > +    const char *oem_id;
> > >       int len = sizeof(*mcfg) + 1 * sizeof(mcfg->allocation[0]);
> > >   
> > >       mcfg = acpi_data_push(table_data, len);
> > > @@ -2431,16 +2433,21 @@ build_mcfg_q35(GArray *table_data, BIOSLinker *linker, 
> > > AcpiMcfgInfo *info)
> > >       /* MCFG is used for ECAM which can be enabled or disabled by guest.
> > >        * To avoid table size changes (which create migration issues),
> > >        * always create the table even if there are no allocations,
> > > -     * but set the signature to a reserved value in this case.
> > > -     * ACPI spec requires OSPMs to ignore such tables.
> > > +     * but fill it with Noop values.
> > > +     * OSPMs ignore such tables.
> > >        */
> > >       if (info->mcfg_base == PCIE_BASE_ADDR_UNMAPPED) {
> > > -        /* Reserved signature: ignored by OSPM */
> > > -        sig = "QEMU";
> > > +        sig = "SSDT";
> > > +        oem = "QEMU ";
> > > +        oem_id = "NOOP";
> > > +        /* 0xa3 - NoopOp */
> > > +        memset(&mcfg->reserved, 0xa3, len - offsetof(AcpiTableMcfg, reserved));
> > >       } else {
> > >           sig = "MCFG";
> > > +        oem = NULL;
> > > +        oem_id = NULL;
> > >       }
> > > -    build_header(linker, table_data, (void *)mcfg, sig, len, 1, NULL, NULL);
> > > +    build_header(linker, table_data, (void *)mcfg, sig, len, 1, oem, oem_id);
> > >   }
> > >   
> > >   /*