Re: [PATCH 2/2] arm/acpi: fix an out of spec _UID for PCI root

[Igor Mammedov]

On Thu, 30 Jul 2020 11:58:41 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On ARM/virt machine type QEMU currently reports an incorrect _UID in
> ACPI.
> 
> The particular node in question is the primary PciRoot (PCI0 in ACPI),
> which gets assigned PCI0 in ACPI UID and 0 in the
> DevicePath. This is due to the _UID assigned to it by build_dsdt in
> hw/arm/virt-acpi-build.c Which does not correspond to the primary PCI
> identifier given by pcibus_num in hw/pci/pci.c
> 
> 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.)
> 
> A similar bug has been reported on i386, on that architecture it has
> been reported to confuse at least macOS which uses ACPI UIDs to build
> the DevicePath for NVRAM boot options, while OVMF firmware gets them via
> an internal channel through QEMU.  When UEFI firmware and ACPI have
> different values, this makes the underlying operating system unable to
> report its boot option.
> 
> Reported-by: vit9696 <vit9696@protonmail.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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

> ---
> 
> Peter can you either ack or merge this one pls?
> 
>  hw/arm/virt-acpi-build.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 91f0df7b13..0a482ff6f7 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -170,7 +170,7 @@ static void acpi_dsdt_add_pci(Aml *scope, const 
> MemMapEntry *memmap,
>      aml_append(dev, aml_name_decl("_CID", aml_string("PNP0A03")));
>      aml_append(dev, aml_name_decl("_SEG", aml_int(0)));
>      aml_append(dev, aml_name_decl("_BBN", aml_int(0)));
> -    aml_append(dev, aml_name_decl("_UID", aml_string("PCI0")));
> +    aml_append(dev, aml_name_decl("_UID", aml_int(0)));
>      aml_append(dev, aml_name_decl("_STR", aml_unicode("PCIe 0 Device")));
>      aml_append(dev, aml_name_decl("_CCA", aml_int(1)));
>