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From: Arnd Bergmann <arnd@arndb.de>
Date: Thu, 21 Dec 2017 21:43:20 +0100
Message-ID: <CAK8P3a2TVbrnjN00iZe2R_FNzLB+82BkiekPOwqtt6WDgFw30w@mail.gmail.com>
Subject: Re: [patches] [PATCH] RISC-V: Support built-in dtb
To: Palmer Dabbelt <palmer@sifive.com>
Cc: zongbox@gmail.com, Olof Johansson <olof@lixom.net>, albert@sifive.com,
        Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
        Wesley Terpstra <wesley@sifive.com>, patches@groups.riscv.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        DTML <devicetree@vger.kernel.org>, Zong Li <zong@andestech.com>
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On Thu, Dec 21, 2017 at 9:32 PM, Palmer Dabbelt <palmer@sifive.com> wrote:
> On Wed, 20 Dec 2017 01:14:31 PST (-0800), zongbox@gmail.com wrote:

> I've added Arnd and Olof, in case they have a bit more perspective here.  If
> I'm reading this correctly, there isn't an arm or arm64 option to do this.
> There is an option to built in many DTBs, which makes a lot more sense to me
> as it doesn't tie the kernel to any one particular implementation.  We'd
> need a mechanism for picking the DTB that Linux should use.  We've kicked
> around the idea of:
>
> * Having the bootloader always provide a DTB.
> * Taking a hash of that DTB when booting Linux.
> * Using that hash to look up DTBs that are built in to Linux.
>
> This would allow us to support replacing broken DTBs if they escape into the
> wild, but would still allow us to have a portable kernel.

Having an embedded DTB is only necessary for platforms with a legacy bootloader
that doesn't understand DT at all, you should never need that here.

I would suggest to require each bootloader to provide a way to replace the DTB
with one that gets installed alongside the kernel.

        Arnd