linux-kernel - Re: [PATCH -fixes] riscv: Fix BUILTIN_DTB for sifive and microchip soc

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Message-ID: <CAM4kBBK467AZ-qhmtREe9mr_bp3QcCEptQcFAApnbrvPc6bkuA@mail.gmail.com>
Date:   Fri, 4 Jun 2021 19:45:45 +0200
From:   Vitaly Wool <vitaly.wool@...sulko.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexandre Ghiti <alex@...ti.fr>, Rob Herring <robh+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        DTML <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -fixes] riscv: Fix BUILTIN_DTB for sifive and microchip soc

Hey Arnd,

On Fri, Jun 4, 2021 at 3:18 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, Jun 4, 2021 at 2:06 PM Alexandre Ghiti <alex@...ti.fr> wrote:
> >
> > Fix BUILTIN_DTB config which resulted in a dtb that was actually not built
> > into the Linux image: in the same manner as Canaan soc does, create an object
> > file from the dtb file that will get linked into the Linux image.
> >
> > Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>
> Along the same lines as the comment that Jisheng Zhang made on the fixed
> address, building a dtb into the kernel itself fundamentally breaks generic
> kernel images.
>
> I can understand using it on K210, which is extremely limited and wouldn't
> run a generic kernel anyway, but for normal platforms like microchip and
> sifive, it would be better to disallow CONFIG_BUILTIN_DTB in Kconfig
> and require a non-broken boot loader.

can't quite agree here. If we take XIP, it does make sense to have
BUILTIN_DTB, since 1) this will not be a generic kernel anyway 2) we
may want to skip the bootloader altogether or at least make it as thin
as possible and 3) copying device tree binaries from bootloader to RAM
as opposed to having it handy compiled in the kernel will be just a
waste of RAM.

Best regards,
   Vitaly

>       Arnd
>
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