[U-Boot] [PATCH RESEND 2/2] cmd: fdt: add fdt overlay application subcommand

[Rob Herring]

On Tue, Apr 5, 2016 at 5:03 PM, Pantelis Antoniou
<pantelis.antoniou at konsulko.com> wrote:
> Hi Maxime,
>
>> On Apr 4, 2016, at 11:25 , Maxime Ripard <maxime.ripard at free-electrons.com> wrote:
>>
>> The device tree overlays are a good way to deal with user-modifyable
>> boards or boards with some kind of an expansion mechanism where we can
>> easily plug new board in (like the BBB or the raspberry pi).
>>
>> However, so far, the usual mechanism to deal with it was to have in Linux
>> some driver detecting the expansion boards plugged in and then request
>> these overlays using the firmware interface.
>>
>> That works in most cases, but in some cases, you might want to have the
>> overlays applied before the userspace comes in. Either because the new
>> board requires some kind of an early initialization, or because your root
>> filesystem is accessed through that expansion board.
>>
>> The easiest solution in such a case is to simply have the component before
>> Linux applying that overlay, removing all these drawbacks.
>>

[...]

>> diff --git a/cmd/fdt_overlay.c b/cmd/fdt_overlay.c
>
> This looks it’s general libfdt code.
> It should end up in libfdt/ so that others can use it, and eventually
> be pushed upstream.

+1. It really needs to go into libfdt first to avoid any re-licensing issues.

Another option which Grant has suggested would be to extend the FDT
format to include overlays as a whole. Then the kernel can apply them
during unflattening. This would simplify things on the bootloader
side.

Rob