Proposal: FIT support for extension boards / overlays

[Simon Glass]

+Masahiro Yamada too

On Wed, 13 Dec 2023 at 01:22, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
>
> Hi,
>
> On Tue, Dec 12, 2023 at 4:52 PM Andrew Davis <afd at ti.com> 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.
>
> Indeed.
>
> 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
> files[3].
>
> 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
> setups[4][5]).
>
> [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
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org
>
> 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