linux-kernel - Re: [RFC 0/2] kbuild: Add support to build overlays (%.dtbo)

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Date:   Thu, 7 Jan 2021 12:57:12 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Olof Johansson <olof@...om.net>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Frank Rowand <frowand.list@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bill Mills <bill.mills@...aro.org>, tero.kristo@...il.com
Subject: Re: [RFC 0/2] kbuild: Add support to build overlays (%.dtbo)

On 07-01-21, 14:28, Masahiro Yamada wrote:
> On Wed, Jan 6, 2021 at 12:21 AM Rob Herring <robh+dt@...nel.org> wrote:
> >
> > On Tue, Jan 5, 2021 at 4:24 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > >
> > > Hello,
> > >
> > > Here is an attempt to make some changes in the kernel to allow building
> > > of device tree overlays.
> > >
> > > While at it, I would also like to discuss about how we should mention
> > > the base DT blobs in the Makefiles for the overlays, so they can be
> > > build tested to make sure the overlays apply properly.
> > >
> > > A simple way is to mention that with -base extension, like this:
> > >
> > > $(overlay-file)-base := platform-base.dtb
> > >
> > > Any other preference ?
> 
> Viresh's patch is not enough.
> 
> We will need to change .gitignore
> and scripts/Makefile.dtbinst as well.

Thanks.
 
> In my understanding, the build rule is completely the same
> between .dtb and .dtbo

Right.

> As Rob mentioned, I am not sure if we really need/want
> a separate extension.
> 
> 
> A counter approach is to use an extension like '.ovl.dtb'
> It clarifies it is an overlay fragment without changing
> anything in our build system or the upstream DTC project.
> 
> We use chained extension in some places, for example,
> .dt.yaml for schema yaml files.
> 
> 
> 
> dtb-$(CONFIG_ARCH_FOO) += \
>     foo-board.dtb \
>     foo-overlay1.ovl.dtb \
>     foo-overlay2.ovl.dtb
> 
> 
> Overlay DT source file names must end with '.ovl.dts'

I am fine with any approach that you guys feel is better, .dts or .ovl.dts. I
wanted to start a discussion where we can resolve this and be done with it.

Thanks.

-- 
viresh