Re: OVMF and PCI0 UID

[Michael S. Tsirkin]

On Mon, Jul 20, 2020 at 11:25:58PM +0200, Laszlo Ersek wrote:
> Hi Vitaly,
> 
> adding Igor, Michael, Marcel, and qemu-devel.
> 
> On 07/20/20 11:06, vit9696 wrote:
> > Hello,
> >
> > I discovered an issue with inconsistent QEMU/OVMF device paths, and
> > while I am unsure whether directing this e-mail is appropriate to you,
> > I believe that you likely have the contacts you could forward this
> > e-mail to.
> >
> > macOS uses ACPI UIDs to build the DevicePath for NVRAM boot options,
> > while OVMF firmware gets them via an internal channel through QEMU.
> > Due to a bug in QEMU (or OVMF) currently UEFI firmware and ACPI have
> > different values, and this makes the underlying operating system
> > unable to report its boot option.
> >
> > The particular node in question is the primary PciRoot (PCI0 in ACPI),
> > which for some reason gets assigned 1 in ACPI UID and 0 in the
> > DevicePath. To me this looks like a bug here:
> > https://github.com/qemu/qemu/blob/8f06f22/hw/i386/acpi-build.c#L1511-L1515
> > Which does not correspond to the primary PCI identifier here:
> > https://github.com/qemu/qemu/blob/5a79d10/hw/pci/pci.c#L160-L162
> >
> > Reference with the device paths, OVMF startup logs, and ACPI table
> > dumps (SysReport):
> > https://github.com/acidanthera/bugtracker/issues/1050
> >
> > Would you be able to forward this to the right people or perhaps keep
> > an eye on the issue itself?
> 
> I think you are right.
> 
> In UEFI v2.8, section "10.4.2 Rules with ACPI _HID and _UID" ends with
> the paragraph,
> 
>     Root PCI bridges will use the plug and play ID of PNP0A03, This will
>     be stored in the ACPI Device Path _HID field, or in the Expanded
>     ACPI Device Path _CID field to match the ACPI name space. The _UID
>     in the ACPI Device Path structure must match the _UID in the ACPI
>     name space.
> 
> (See especially the last sentence.)
> 
> Considering *extra* root bridges / root buses (with bus number > 0),
> QEMU's ACPI generator actually does the right thing; since QEMU commit
> c96d9286a6d7 ("i386/acpi-build: more traditional _UID and _HID for PXB
> root buses", 2015-06-11).
> 
> However, the _UID values for root bridge zero (on both i440fx and q35)
> have always been "wrong" (from UEFI perspective), going back in QEMU to
> commit 74523b850189 ("i386: add ACPI table files from seabios",
> 2013-10-14).
> 
> Even in SeaBIOS, these _UID values have always been 1; see commit
> a4d357638c57 ("Port rombios32 code from bochs-bios.", 2008-03-08) for
> i440fx, and commit ecbe3fd61511 ("seabios: q35: add dsdt", 2012-12-01)
> for q35.
> 
> Does the following patch work for you? (I can see you proposed the same
> in
> <https://github.com/acidanthera/bugtracker/issues/1050#issuecomment-660734139>)
> 
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index b7bcbbbb2a35..7a5a8b3521b0 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -1496,9 +1496,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >          sb_scope = aml_scope("_SB");
> >          dev = aml_device("PCI0");
> >          aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
> >          aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
> > -        aml_append(dev, aml_name_decl("_UID", aml_int(1)));
> > +        aml_append(dev, aml_name_decl("_UID", aml_int(0)));
> >          aml_append(sb_scope, dev);
> >          aml_append(dsdt, sb_scope);
> >
> >          build_hpet_aml(dsdt);
> > @@ -1511,9 +1511,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
> >          dev = aml_device("PCI0");
> >          aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A08")));
> >          aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
> >          aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
> > -        aml_append(dev, aml_name_decl("_UID", aml_int(1)));
> > +        aml_append(dev, aml_name_decl("_UID", aml_int(0)));
> >          aml_append(dev, build_q35_osc_method());
> >          aml_append(sb_scope, dev);
> >          aml_append(dsdt, sb_scope);
> 
> If it does, I suggest submitting the above patch to qemu-devel, and/or
> filing a bug for upstream QEMU at <https://bugs.launchpad.net/qemu/>.

Or even just reporting whether the above helps you, we can
take it from there.

> (Note: I didn't even compile the above change.)
> 
> Thanks
> Laszlo