linux-kernel - Re: [PATCH] of: Overlay manager

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Date:   Thu, 8 Sep 2016 20:06:48 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Dmitry Shmidt <dimitrysh@...gle.com>,
        Frank Rowand <frowand.list@...il.com>,
        "<linux-kernel@...r.kernel.org>" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH] of: Overlay manager

On Thu, Sep 8, 2016 at 7:27 PM, Rob Herring <robh+dt@...nel.org> wrote:
> On Thu, Sep 8, 2016 at 7:39 PM, John Stultz <john.stultz@...aro.org> wrote:
>> On Thu, Sep 8, 2016 at 5:33 PM, Rob Herring <robh+dt@...nel.org> wrote:
>>> If you can figure out how to change the command line, then you can
>>> just change the dtb. At least for how Android boot works, those aren't
>>> really changed separately.
>>
>> Ehh.. that's not so simple. The dtb is often appended to the kernel on
>> Android devices. Changing the boot arguments is much simpler to do.
>
> How? You typically make a new bootimage assembling the kernel/dtb,
> ramdisk and kernel command-line. If things were done differently such
> that the dtb is part of the bootloader (how it is supposed to be
> done), then I would buy the argument that we can't update the dtb and
> need to either have a way to add and/or select overlays. But Android
> folks like to update *everything*, so I don't buy that here.

So in many cases the dtb is appended when the kernel is built, not
when the abootimg is assembled.

So its much easier to use abootimg -u to update a prebuilt boot.img in
place and reflash. That way users don't need to regenerate the kernel
w/ appended dtb.

thanks
-john