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

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Message-ID: <20210310144121.74mawocx2ydgabx2@vireshk-i7>
Date:   Wed, 10 Mar 2021 20:11:21 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Masahiro Yamada <masahiroy@...nel.org>, robh+dt@...nel.org
Cc:     linux-kbuild@...r.kernel.org, devicetree@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: remove unneeded -O option to dtc

On 10-03-21, 20:08, Masahiro Yamada 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);

Looking at the very first version of the patch I sent,

https://lore.kernel.org/lkml/7aa70809eff3f32d821761d2a763e4fb72ecc8fb.1609844956.git.viresh.kumar@linaro.org/

this change was the only thing that was required to make it work.

I think the reason was that "outform != NULL" as -O option was passed
by the kernel.

> 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)

LGTM.

Reviewed-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh