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

[Igor Mammedov]

On Fri, 30 Oct 2020 10:50:01 +0800
Ying Fang <fangying1@huawei.com> wrote:

> Hi,
> 
> I have a question on UEFI/ACPI tables setup and probing on arm64 platform.

CCing Laszlo,
who might know how it's implemented.
 
> Currently on arm64 platform guest can be booted with both fdt and ACPI
> supported. If ACPI is enabled, [1] says the only defined method for
> passing ACPI tables to the kernel is via the UEFI system configuration
> table. So AFAIK, ACPI Should be dependent on UEFI.
> 
> What's more [2] says UEFI kernel support on the ARM architectures
> is only available through a *stub*. The stub populates the FDT /chosen
> node with some UEFI parameters describing the UEFI location info.
> 
> So i dump /sys/firmware/fdt from the guest, it does have something like:
> 
> /dts-v1/;
> 
> / {
>       #size-cells = <0x02>;
>       #address-cells = <0x02>;
> 
>       chosen {
>               linux,uefi-mmap-desc-ver = <0x01>;
>               linux,uefi-mmap-desc-size = <0x30>;
>               linux,uefi-mmap-size = <0x810>;
>               linux,uefi-mmap-start = <0x04 0x3c0ce018>;
>               linux,uefi-system-table = <0x04 0x3f8b0018>;
>               bootargs = 
> "BOOT_IMAGE=/vmlinuz-4.19.90-2003.4.0.0036.oe1.aarch64 
> root=/dev/mapper/openeuler-root ro rd.lvm.lv=openeuler/root 
> rd.lvm.lv=openeuler/swap video=VGA-1:640x480-32@60me 
> smmu.bypassdev=0x1000:0x17 smmu.bypassdev=0x1000:0x15 
> crashkernel=1024M,high video=efifb:off video=VGA-1:640x480-32@60me";
>               linux,initrd-end = <0x04 0x3a85a5da>;
>               linux,initrd-start = <0x04 0x392f2000>;
>       };
> };
> 
> But the question is that I did not see any code adding the uefi
> in fdt chosen node in *arm_load_dtb* or anywhere else.
> Qemu only maps the OVMF binary file into a pflash device.
> So I'm really confused on how UEFI information is provided to
> guest by qemu. Does anybody know of the details about it ?
> 
> [1] https://www.kernel.org/doc/html/latest/arm64/arm-acpi.html
> [2] https://www.kernel.org/doc/Documentation/arm/uefi.rst
> 
> Thanks.
> Ying
>