linux-kernel - Re: [PATCH] kbuild: remove unneeded -O option to dtc

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Date:   Wed, 10 Mar 2021 09:54:36 -0700
From:   Rob Herring <robh@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        devicetree@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: remove unneeded -O option to dtc

On Wed, Mar 10, 2021 at 4:09 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> This piece of code converts the target suffix to the dtc -O option:
>
>     *.dtb      ->  -O dtb
>     *.dt.yaml  ->  -O yaml
>
> Commit ce88c9c79455 ("kbuild: Add support to build overlays (%.dtbo)")
> added the third case:
>
>     *.dtbo     ->  -O dtbo
>
> This works thanks to commit 163f0469bf2e ("dtc: Allow overlays to have
> .dtbo extension") in the upstream DTC, which has already been pulled in
> the kernel.
>
> However, I think it is a bit odd because "dtbo" is not a format name.
> At least, it does not show up in the help message of dtc.
>
> $ scripts/dtc/dtc --help
>   [ snip ]
>   -O, --out-format <arg>
>         Output formats are:
>                 dts - device tree source text
>                 dtb - device tree blob
>                 yaml - device tree encoded as YAML
>                 asm - assembler source
>
> So, I am not a big fan of the second hunk of that change:
>
>         } else if (streq(outform, "dtbo")) {
>                 dt_to_blob(outf, dti, outversion);
>
> Anyway, we did not need to do this in Makefile in the first place.
>
> guess_type_by_name() had already understood ".yaml" before commit
> 4f0e3a57d6eb ("kbuild: Add support for DT binding schema checks"),
> and now does ".dtbo" as well.
>
> Makefile does not need to duplicate the same logic. Let's leave it
> to dtc.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  scripts/Makefile.lib | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index eee59184de64..90a4e04cd8f5 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -327,7 +327,7 @@ $(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 $@ -b 0 \
>                 $(addprefix -i,$(dir $<) $(DTC_INCLUDE)) $(DTC_FLAGS) \
>                 -d $(depfile).dtc.tmp $(dtc-tmp) ; \
>         cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)

I think you should also drop 'yaml' from:

$(call if_changed_rule,dtc,yaml)

Though that's somewhat separate, so either way:

Acked-by: Rob Herring <robh@...nel.org>

Rob