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

From: Masahiro Yamada <masahiroy@kernel.org>
To: "Uwe Kleine-König" <uwe@kleine-koenig.org>
Cc: 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>
Subject: Re: [PATCH] cmd_dtc: Enable generation of device tree symbols
Date: Tue, 26 Jan 2021 06:53:22 +0900	[thread overview]
Message-ID: <CAK7LNAS5t1wew0MMFjdB5HGCAMerhU7pAGiFhcTtCRUAAjGLpw@mail.gmail.com> (raw)
In-Reply-To: <20210125105757.661240-1-uwe@kleine-koenig.org>

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.)

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."

> ---
>  scripts/Makefile.lib | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 213677a5ed33..0683a5808f7f 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -319,7 +319,7 @@ $(obj)/%.dtb.S: $(obj)/%.dtb FORCE
>
>  quiet_cmd_dtc = DTC     $@
>  cmd_dtc = $(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
> -       $(DTC) -O $(patsubst .%,%,$(suffix $@)) -o $@ -b 0 \
> +       $(DTC) -@ -O $(patsubst .%,%,$(suffix $@)) -o $@ -b 0 \
>                 $(addprefix -i,$(dir $<) $(DTC_INCLUDE)) $(DTC_FLAGS) \
>                 -d $(depfile).dtc.tmp $(dtc-tmp) ; \
>         cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)
> --
> 2.29.2
>

--
Best Regards

Masahiro Yamada