Re: Question on UEFI ACPI tables setup and probing on arm64

[Laszlo Ersek]

On 11/05/20 05:30, Ying Fang wrote:

> I see it in Qemu the *loader_start* is fixed at 1 GiB on the
> physical address space which points to the DRAM base. In ArmVirtQemu.dsc
> PcdDeviceTreeInitialBaseAddress is set 0x40000000 with correspondence.
> 
> Here I also see the discussion about DRAM base for ArmVirtQemu.
> https://lists.gnu.org/archive/html/qemu-devel/2017-10/msg03127.html
> 
> I am still not sure how UEFI knows that it is running on a ArmVirtQemu
> machine type.

It doesn't know. It remains a convention.

This part is not auto-detected; the constants in QEMU and edk2 are
independently open-coded, their values were synchronized by human effort
initially.

The user or the management layer have to make sure they boot a UEFI
firmware binary on the machine type that is compatible with the machine
type.

There is some meta-data to help with that:

> Does UEFI derive it from the fdt *compatible* property ?

Please see the schema "docs/interop/firmware.json" in the QEMU tree; in
particular the @FirmwareTarget element.

For an actual example: QEMU bundles some edk2 firmware binaries (purely
as a convenience, not for production), and those are accompanied by
matching descriptor files. See
"pc-bios/descriptors/60-edk2-aarch64.json". (It is a template that's
fixed up during QEMU installation, but that's tangential here.)

    "targets": [
        {
            "architecture": "aarch64",
            "machines": [
                "virt-*"
            ]
        }
    ],

Thanks
Laszlo