Re: [PATCH 1/2] i386/acpi: fix inconsistent QEMU/OVMF device paths

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 30 Jul 2020 11:58:38 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> 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 ACPI 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. This is due to the _UID assigned to it by build_dsdt in
> hw/i386/acpi-build.c Which does not correspond to the primary PCI
> identifier given by pcibus_num in hw/pci/pci.c
> 
> Reference with the device paths, OVMF startup logs, and ACPI table
> dumps (SysReport):
> https://github.com/acidanthera/bugtracker/issues/1050
> 
> 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.
> 
> Suggested-by: Laszlo Ersek <lersek@redhat.com>
> Tested-by: vit9696 <vit9696@protonmail.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Reviewed-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  hw/i386/acpi-build.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index b7bcbbbb2a..7a5a8b3521 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -1497,7 +1497,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
>          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);
>  
> @@ -1512,7 +1512,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
>          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);