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

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Message-ID: <20210205210814.GA3707622@robh.at.kernel.org>
Date:   Fri, 5 Feb 2021 15:08:14 -0600
From:   Rob Herring <robh@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Frank Rowand <frowand.list@...il.com>,
        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)

On Fri, Feb 05, 2021 at 11:17:10AM +0100, Geert Uytterhoeven wrote:
> 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.

I think what Viresh means is dtc won't automatically set the input type 
to dts if not .dts.

We stuck with .dtbo as it's already widely used. I don't know about 
dtso though. If there's strong consensus to use .dtso, then let's do 
that. Whatever color for this shed you like.

Rob