Re: [PATCH] of: Overlay manager

[John Stultz]

On Thu, Sep 8, 2016 at 7:27 PM, Rob Herring <robh+dt@xxxxxxxxxx> wrote:
> On Thu, Sep 8, 2016 at 7:39 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
>> On Thu, Sep 8, 2016 at 5:33 PM, Rob Herring <robh+dt@xxxxxxxxxx> 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