linux-kernel - Re: [PATCH V7 4/6] kbuild: Add support to build overlays (%.dtbo)

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Date:   Fri, 5 Feb 2021 11:17:10 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        anmar.oueja@...aro.org, Bill Mills <bill.mills@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH V7 4/6] kbuild: Add support to build overlays (%.dtbo)

Hi Viresh,

On Fri, Feb 5, 2021 at 10:55 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 05-02-21, 10:41, Geert Uytterhoeven wrote:
> > On Fri, Feb 5, 2021 at 10:25 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > > On 05-02-21, 10:02, Geert Uytterhoeven wrote:
> > > > Thanks for your patch
> > > > (which I only noticed because it appeared in dt-rh/for-next ;-)
> > > >
> > > > On Fri, Jan 29, 2021 at 8:31 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > > > > Add support for building DT overlays (%.dtbo). The overlay's source file
> > > > > will have the usual extension, i.e. .dts, though the blob will have
> > > >
> > > > Why use .dts and not .dtso for overlays?
> > > > Because you originally (until v5) had a single rule for building .dtb
> > > > and .dtbo files?
> > >
> > > I am fine with doing that as well if Rob and David agree to it. Rob
> > > did suggest that at one point but we didn't do much about it later on
> > > for some reason.
> > >
> > > FWIW, this will also require a change in the DTC compiler.
> >
> > Care to explain why? I've been using .dtsi for ages in
> > https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/log/?h=topic/renesas-overlays
>
> I don't see you building them anywhere, they aren't added to the
> Makefile ever. What am I missing ?
>
> actually none of the dtso's were added to any makefile in that branch.

E.g. "ARM: dts: Build all overlays if OF_OVERLAY=y"?
https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/commit/?h=topic/renesas-overlays&id=597ee90971687a45678cca8d16bf624d174a99eb

> Anyway, the DTC needs to know how to treat the dtso format and it will
> error out currently with unknown format kind of errors.
>
> Below email [1] have some information on the kind of changes required
> here. Also note that we had to do similar changes for dtbo earlier
> [2].
>
> --
> viresh
>
> [1] https://lore.kernel.org/lkml/CAK7LNASViCOTGR7yDTfh0O+PAu+X-P2NwdY4oPMuXrr51awafA@mail.gmail.com/

-@ is handled by "kbuild: Enable DT symbols when CONFIG_OF_OVERLAY is used"
https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/commit/?h=topic/renesas-overlays&id=91e9d998514f3743125a707013a30d5f83054579

> [2] https://lore.kernel.org/lkml/30fd0e5f2156665c713cf191c5fea9a5548360c0.1609926856.git.viresh.kumar@linaro.org/

I never had a need for those changes to dtc. .dtso/.dtbo work fine regardless.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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