Re: [PATCH] cmd_dtc: Enable generation of device tree symbols

From: Rob Herring <robh@kernel.org>
To: "Uwe Kleine-König" <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>
Subject: Re: [PATCH] cmd_dtc: Enable generation of device tree symbols
Date: Tue, 26 Jan 2021 07:42:48 -0600	[thread overview]
Message-ID: <CAL_JsqJQjnNULke5uyNbrj5kkS=3MSxug2BFXAia1ucyaDhx5Q@mail.gmail.com> (raw)
In-Reply-To: <9d9bb0f6-d4f4-b1b9-a4c4-786987578085@kleine-koenig.org>

On Tue, Jan 26, 2021 at 1:27 AM Uwe Kleine-König <uwe@kleine-koenig.org> wrote:
>
> Hello Masahiro,
>
> On 1/25/21 10:53 PM, Masahiro Yamada wrote:
> > On Mon, Jan 25, 2021 at 8:07 PM Uwe Kleine-König <uwe@kleine-koenig.org> wrote:
> >>
> >> Adding the -@ switch to dtc results in the binary devicetrees containing
> >> 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-König <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