linux-kernel - Re: [patches] [PATCH] RISC-V: Support built-in dtb

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Date:   Thu, 21 Dec 2017 21:43:20 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     zongbox@...il.com, Olof Johansson <olof@...om.net>,
        albert@...ive.com, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Wesley Terpstra <wesley@...ive.com>, patches@...ups.riscv.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>, Zong Li <zong@...estech.com>
Subject: Re: [patches] [PATCH] RISC-V: Support built-in dtb

On Thu, Dec 21, 2017 at 9:32 PM, Palmer Dabbelt <palmer@...ive.com> wrote:
> On Wed, 20 Dec 2017 01:14:31 PST (-0800), zongbox@...il.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