linux-kernel - Re: [PATCH] OF: Add support for built in FDT blob

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Message-ID: <CAL_Jsq+n8owZz6yas=surm4fTaGWgUuCLLEKXYKm8_02S8DdYA@mail.gmail.com>
Date:	Fri, 7 Nov 2014 08:56:32 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Alban <albeu@...e.fr>
Cc:	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [PATCH] OF: Add support for built in FDT blob

On Fri, Nov 7, 2014 at 6:59 AM, Alban <albeu@...e.fr> wrote:
> On Fri, 7 Nov 2014 12:09:33 +0000
> Mark Rutland <mark.rutland@....com> wrote:
>
>> Hi,
>>
>> On Fri, Nov 07, 2014 at 11:14:09AM +0000, Alban Bedel wrote:
>> > Allow embedding an FDT blob in the kernel image, this is mostly
>> > useful to run new kernels on boards with old bootloaders.
>>
>> I am very much not keen on embedding a DTB within a kernel. It's far
>> nicer for the two to remain separate blobs, with a small shim to set
>> up the DTB address.
>>
>> On ARM we have appended DTB for this purpose, which is at least better
>> than embedding the DT inside of the kernel.
>
> I looked at that but that seemed quiet complicated to implement, not to
> mention that it needed quiet a lot of arch specific code. On the other
> hand having the DTB built in like this was trivial and would be portable
> to every architecture, so that seemed like the best way to me.
>
>> What architecture and bootloader are you using that necessitate this?
>
> MIPS with an antic u-boot version patched by the board vendor to use
> some non standard image format. Updating the boot loader is currently
> not an option because of the lack of documentation for the board/SoC.

MIPS and a few other arches already have built-in dtb support. We
don't need another way to do it, but I would welcome any clean-up that
makes it arch independent and available to any arch.

While Mark is right, I could envision other uses such as embedding
overlay dtbs in the kernel either for add-on boards or just as fixups.

Rob
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