linux-kernel - Re: [PATCH V7 1/3] kbuild: Add generic rule to apply fdtoverlay

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Date:   Fri, 12 Feb 2021 12:07:00 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Anmar Oueja <anmar.oueja@...aro.org>,
        Bill Mills <bill.mills@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH V7 1/3] kbuild: Add generic rule to apply fdtoverlay

On Fri, Feb 12, 2021 at 5:05 AM Rob Herring <robh+dt@...nel.org> wrote:
>
> On Thu, Feb 11, 2021 at 12:28 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > On Wed, Feb 10, 2021 at 8:13 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > >
> > > From: Rob Herring <robh@...nel.org>
> > >
> > > Add a generic rule to apply fdtoverlay in Makefile.lib, so every
> > > platform doesn't need to carry the complex rule.
> > >
> > > The platform's Makefile only needs to have this now:
> > >
> > >  DTC_FLAGS_foo_base += -@
> > >  foo-dtbs := foo_base.dtb foo_overlay1.dtbo foo_overlay2.dtbo
> > >  overlay-y := foo.dtb
> >
> >
> > Please reuse dtb-y instead of introducing the new
> > overlay-y syntax, that is,
> >
> > foo-dtbs := foo_base.dtb foo_overlay1.dtbo foo_overlay2.dtbo
> > dtb-y := foo.dtb
>
> That's what I had, but I believe Viresh changed this because we don't
> want to run schema checks on foo.dtb (as foo.dts doesn't exist).
> However, we should be able to filter those out using something similar
> to technique used for multi-used-y and real-obj-y. We just need to
> drop composite entries when creating the .dt.yaml list.



Yes, I think this will work.



BTW, I do not know how to use overlay.
Do we apply overlay in the build time?
If so, I do not know what the benefit of overlay is.
Or is this just for build testing?


I just thought this was done in the boot time,
for example, in U-Boot or something.




-- 
Best Regards
Masahiro Yamada