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From:   Rob Herring <robh@kernel.org>
Date:   Tue, 26 Jan 2021 07:42:48 -0600
Message-ID: <CAL_JsqJQjnNULke5uyNbrj5kkS=3MSxug2BFXAia1ucyaDhx5Q@mail.gmail.com>
Subject: Re: [PATCH] cmd_dtc: Enable generation of device tree symbols
To:     =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= <uwe@kleine-koenig.org>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        cyril@debamax.com, Arnd Bergmann <arnd@arndb.de>,
        Maxime Ripard <mripard@kernel.org>,
        DTML <devicetree@vger.kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Frank Rowand <frowand.list@gmail.com>
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On Tue, Jan 26, 2021 at 1:27 AM Uwe Kleine-K=C3=B6nig <uwe@kleine-koenig.or=
g> wrote:
>
> Hello Masahiro,
>
> On 1/25/21 10:53 PM, Masahiro Yamada wrote:
> > On Mon, Jan 25, 2021 at 8:07 PM Uwe Kleine-K=C3=B6nig <uwe@kleine-koeni=
g.org> wrote:
> >>
> >> Adding the -@ switch to dtc results in the binary devicetrees containi=
ng
> >> a list of symbolic references and their paths. This is necessary to
> >> apply device tree overlays e.g. on Raspberry Pi as described on
> >> https://www.raspberrypi.org/documentation/configuration/device-tree.md=
.
> >>
> >> Obviously the downside of this change is an increas of the size of the
> >> generated dtbs, for an arm out-of-tree build (multi_v7_defconfig):
> >>
> >>          $ du -s arch/arm/boot/dts*
> >>          101380  arch/arm/boot/dts-pre
> >>          114308  arch/arm/boot/dts-post
> >>
> >> so this is in average an increase of 12.8% in size.
> >>
> >> Signed-off-by: Uwe Kleine-K=C3=B6nig <uwe@kleine-koenig.org>
> >
> >
> > (CCing DT ML.)
>
> makes sense, thanks.
>
> > https://www.spinics.net/lists/linux-kbuild/msg27904.html
> >
> > See Rob's comment:
> >
> > "We've already rejected doing that. Turning on '-@' can grow the dtb
> > size by a significant amount which could be problematic for some
> > boards."
>
> The patch was created after some conversation on irc which continued
> after I sent the patch. I added the participating parties to Cc:.
>
> The (relevant) followups were:
>
> Geert suggested to always generate the symbols and provide a way to
> strip the symbols for installation if and when they are not needed.
>
> Rob said: "I'm less concerned with the size increases, but rather that
> labels go from purely source syntax to an ABI. I'd rather see some
> decision as to which labels are enabled or not."

I've also said move the arm32 dts files to family subdirectories and
enable '-@' per directory. I've posted a script to do the whole thing,
but I think the preference is one-by-one. This is needed anyways if
we're going to start adding overlays which Viresh is working on.

Rob