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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Mon, 28 Feb 2022 12:35:00 +0100
Message-ID: <CAMj1kXHGG80LdNUUA+Ug1VBXWuvtPxKpqnuChg2N=6Hf2EhY7g@mail.gmail.com>
Subject: Re: [PATCH V6 09/22] LoongArch: Add boot and setup routines
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Huacai Chen <chenhuacai@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Huacai Chen <chenhuacai@loongson.cn>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>, Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Airlie <airlied@linux.ie>,
        Jonathan Corbet <corbet@lwn.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Xuefeng Li <lixuefeng@loongson.cn>,
        Yanteng Si <siyanteng@loongson.cn>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        linux-efi <linux-efi@vger.kernel.org>
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On Mon, 28 Feb 2022 at 12:24, Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Mon, Feb 28, 2022 at 11:42 AM Huacai Chen <chenhuacai@gmail.com> wrote:
> > On Mon, Feb 28, 2022 at 4:52 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > > On Mon, 28 Feb 2022 at 09:38, Huacai Chen <chenhuacai@gmail.com> wrote:
> > > > >
> > > > > RISC-V is a useful reference for the changes needed - this is the most
> > > > > recent addition to the EFI stub, and avoids some legacy stuff that new
> > > > > architectures have no need for.
> > > > We still want to support the raw elf kernel (RISC-V also does),
> > > > because LoongArch also has MCU and SoC and we want to support FDT (I
> > > > think this is reasonable, because RISC-V also supports raw elf).
> > > >
> > >
> > > That is fine. So perhaps the best course of action is to omit the
> > > UEFI/ACPI parts entirely for now, and focus on the DT/embedded use
> > > case. Once all the spec pieces are in place, the UEFI + ACPI changes
> > > can be presented as a single coherent set.
> > It seems that I made you confusing. :)
> > There are big CPUs and small CPUs (MCU and SoC), big CPUs use
> > UEFI+ACPI, while small CPUs use FDT.
> > At present, the only matured LoongArch CPU is Loongson-3A5000 (big
> > CPU) which uses UEFI+ACPI.
> > We want to support raw elf because it can run on both ACPI firmware
> > and FDT firmware, but at present we only have ACPI firmware.
>
> Can't you just use the UEFI protocol for kernel entry regardless
> of the bootloader? It seems odd to use a different protocol for loading
> grub and the kernel, especially if that means you end up having to
> support both protocols inside of u-boot and grub, in order to chain-load
> a uefi application like grub.
>

I think this would make sense. Now that the EFI stub has generic
support for loading the initrd via a UEFI specific protocol (of which
u-boot already carries an implementation), booting via UEFI only would
mean that no Linux boot protocol would need to be defined outside of
the kernel at all (i.e., where to load the kernel, where to put the
command line, where to put the initrd, other arch specific rules etc
etc) UEFI already supports both ACPI and DT boot