Proposal: FIT support for extension boards / overlays

Geert Uytterhoeven geert at
Wed Dec 13 09:22:07 CET 2023


On Tue, Dec 12, 2023 at 4:52 PM Andrew Davis <afd at> wrote:
> On 12/12/23 8:05 AM, Simon Glass wrote:
> > The devicetree files for a board can be quite large, perhaps around
> > 60KB. To boot on any supported board, many of them need to be
> > provided, typically hundreds.
> >
> > All boards for a particular SoC share common parts.  It would be
> > helpful to use overlays for common pieces, to reduce the overall size.
> >
> For this to save much size we would need to have the SoC split
> from each board that uses it. We don't have that in DT today.
> There are some efforts in progress to help on this but until
> then we will not get much here.


E.g. The Kingfisher board[1] is an extension for (various) ULCB
boards[2], but we cannot use an overlay for the former, as the
combinations need to have different top-level compatible (and model)
values.  Hence currently we use a .dtsi file and lots of extra .dts

The other issue is the need for parameterization, due to slight
differences in pins/signals on various base boards, or because the
same connector is present multiple times (e.g. for multi-camera

[1] arch/arm64/boot/dts/renesas/ulcb-kf.dtsi
[2] arch/arm64/boot/dts/renesas/*-ulcb.dts
[3] arch/arm64/boot/dts/renesas/*-ulcb-kf.dts
[4] arch/arm/boot/dts/renesas/r8a7742-iwg21d-q7-dbcm-ov5640-single.dtsi
[5] arch/arm/boot/dts/renesas/r8a7742-iwg21d-q7-dbcm-ov7725-single.dtsi



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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