Re: [PATCH v3 4/4] dt-bindings: firmware: Document ffitbl binding

[Conor Dooley <conor@kernel.org>]

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Hey,

On Wed, Jul 05, 2023 at 07:42:51PM +0800, Yunhui Cui wrote:
> Add the description for ffitbl subnode.
> 
> Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
> ---
>  .../devicetree/bindings/firmware/ffitbl.txt   | 27 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  2 files changed, 28 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/firmware/ffitbl.txt
> 
> diff --git a/Documentation/devicetree/bindings/firmware/ffitbl.txt b/Documentation/devicetree/bindings/firmware/ffitbl.txt
> new file mode 100644
> index 000000000000..c42368626199
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/ffitbl.txt
> @@ -0,0 +1,27 @@
> +FFI(FDT FIRMWARE INTERFACE) driver
> +
> +Required properties:
> + - entry		: acpi or smbios root pointer, u64
> + - reg			: acpi or smbios version, u32
> +
> +Some bootloaders, such as Coreboot do not support EFI,
> +only devicetree and some arches do not have a reserved
> +address segment. Add "ffitbl" subnode to obtain ACPI RSDP
> +and SMBIOS entry.

Since the conversation on this stuff all seems to be going absolutely
nowhere, the ACPI portion of this is intended for use on RISC-V in
violation of the RISC-V ACPI specs. It also goes against the
requirements of the platform spec. Quoting from [1]:

| > Just so we're all on the same page, I just now asked Mark Himelstein
| > of RISC-V International if there is anything in RISC-V standards that
| > requires UEFI, and the answer is a solid "no."
| 
| Huh? Firstly, running off to invoke RVI is not productive - they don't
| maintain the various operating system kernels etc.
| Secondly, that does not seem to be true. The platform spec mandates UEFI
| for the OS-A server platform, alongside ACPI:
| https://github.com/riscv/riscv-platform-specs/blob/main/riscv-platform-spec.adoc#32-boot-process
| and the OS-A embedded platform needs to comply with EBBR & use DT:
| https://github.com/riscv/riscv-platform-specs/blob/main/riscv-platform-spec.adoc#32-boot-process
| 
| EBBR does say that systems must not provide both ACPI and DT to the OS
| loader, but I am far from an expert on these kind of things & am not
| sure where something like this where the DT "contains" ACPI would stand.
| 
| The RISC-V ACPI spec also says "UEFI firmware is mandatory to support
| ACPI":
| https://github.com/riscv-non-isa/riscv-acpi/blob/master/riscv-acpi-guidance.adoc

NAKed-by: Conor Dooley <conor.dooley@microchip.com>

Cheers,
Conor.

[1] - https://lore.kernel.org/linux-riscv/20230707-attach-conjuror-306d967347ce@wendy/

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