linux-kernel - Re: [External] [PATCH v2 1/3] riscv: obtain ACPI RSDP from FFI.

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Message-ID: <87bkgql8rq.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 05 Jul 2023 16:42:33 +0200
From:   Björn Töpel <bjorn@...nel.org>
To:     运辉崔 <cuiyunhui@...edance.com>,
        Jessica Clarke <jrtc27@...c27.com>,
        Emil Renner Berthing <emil.renner.berthing@...il.com>
Cc:     Andrew Jones <ajones@...tanamicro.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        rminnich@...il.com, Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, jdelvare@...e.com,
        yc.hung@...iatek.com, angelogioacchino.delregno@...labora.com,
        allen-kh.cheng@...iatek.com, pierre-louis.bossart@...ux.intel.com,
        tinghan.shen@...iatek.com,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-acpi@...r.kernel.org, geshijian@...edance.com,
        weidong.wd@...edance.com
Subject: Re: [External] [PATCH v2 1/3] riscv: obtain ACPI RSDP from FFI.

Jessica Clarke <jrtc27@...c27.com> writes:

> On 3 Jul 2023, at 19:58, Emil Renner Berthing <emil.renner.berthing@...il.com> wrote:
>> 
>> On Mon, 3 Jul 2023 at 15:33, 运辉崔 <cuiyunhui@...edance.com> wrote:
>>> 
>>> Hi drew,
>>> 
>>> On Mon, Jul 3, 2023 at 9:01 PM Andrew Jones <ajones@...tanamicro.com> wrote:
>>>> 
>>>> 
>>>> (This is a reply to a non-existent cover letter.)
>>> 
>>> This has been discussed many times with Ard, Please refer to :
>>> https://patches.linaro.org/project/linux-acpi/patch/20230426034001.16-1-cuiyunhui@bytedance.com/
>> 
>> Hi Yunhui,
>> 
>> From that discussion it was mentioned that that arm supports 3 methods
>> of booting:
>>  direct + devicetree
>>  EFI + devicetree
>>  EFI + ACPI
>> ..but not
>>  direct + ACPI
>> 
>> To me it isn't obvious from that or this thread, and since arm seems
>> to be doing fine without the 4th option I'm curious why that's
>> necessary on riscv?
>
> If anything we should be removing option 1, because that’s not a
> cross-OS standard (though RISC-V’s SBI direct booting is at least not
> tied to the OS). Any application-class platform spec is going to
> mandate EFI, because, whatever your thoughts of EFI are, that is *the*
> standard. And if you’re willing to pick up all the complexity of ACPI,
> what’s a bit of EFI (especially if you only go for a minimal one a la
> U-Boot)?

Well said!

Yunhui, why not simply add a minimal UEFI stub to Coreboot (like Jess
points out above)?

IMO what U-boot (or
https://github.com/cloud-hypervisor/rust-hypervisor-firmware if you're
into Rust ;-)) is doing, and just having a small UEFI shim is the way to
go.