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

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Message-ID: <mhng-40be3873-485c-4cb6-9990-1137745f5425@palmer-si-x1c4>
Date:   Thu, 21 Dec 2017 12:48:05 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     zongbox@...il.com, Olof Johansson <olof@...om.net>,
        albert@...ive.com, robh+dt@...nel.org, mark.rutland@....com,
        Wesley Terpstra <wesley@...ive.com>, patches@...ups.riscv.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        zong@...estech.com
Subject:     Re: [patches] [PATCH] RISC-V: Support built-in dtb

On Thu, 21 Dec 2017 12:43:20 PST (-0800), Arnd Bergmann wrote:
> 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.

Sounds good to me.