linux-kernel - Re: [PATCH V6 09/22] LoongArch: Add boot and setup routines

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Date:   Mon, 28 Feb 2022 12:24:23 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Huacai Chen <chenhuacai@...il.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH V6 09/22] LoongArch: Add boot and setup routines

On Mon, Feb 28, 2022 at 11:42 AM Huacai Chen <chenhuacai@...il.com> wrote:
> On Mon, Feb 28, 2022 at 4:52 PM Ard Biesheuvel <ardb@...nel.org> wrote:
> > On Mon, 28 Feb 2022 at 09:38, Huacai Chen <chenhuacai@...il.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.

       Arnd