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From: Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] kbuild: avoid unrecognized option error for external DTC
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References: <1488174052-2530-1-git-send-email-yamada.masahiro@socionext.com> <1488204416.2819.9.camel@decadent.org.uk>
Date: Tue, 28 Feb 2017 21:21:02 +1100
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To: Ben Hutchings <ben@decadent.org.uk>, Masahiro Yamada <yamada.masahiro@socionext.com>, linux-kbuild@vger.kernel.org
Cc: Alessio Igor Bogani <alessio.bogani@elettra.eu>, Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>, linux-c6x-dev@linux-c6x.org, Michal Simek <monstr@monstr.eu>, Nicolas Pitre <nicolas.pitre@linaro.org>, Marcin Nowakowski <marcin.nowakowski@imgtec.com>, devicetree@vger.kernel.org, Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>, Michal Marek <mmarek@suse.com>, Scott Wood <oss@buserror.net>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, linuxppc-dev@lists.ozlabs.org, Paul Mackerras <paulus@samba.org>, openrisc@lists.librecores.org, Mark Salter <msalter@redhat.com>, Stafford Horne <shorne@gmail.com>, Aurelien Jacquiot <a-jacquiot@ti.com>, Jonas Bonn <jonas@southpole.se>, linux-kernel@vger.kernel.org, Oliver O'Halloran <oohall@gmail.com>, Mark Rutland <mark.rutland@arm.com>, Emese Revfy <re.emese@gmail.com>

Ben Hutchings <ben@decadent.org.uk> writes:

> [ Unknown signature status ]
> On Mon, 2017-02-27 at 14:40 +0900, Masahiro Yamada wrote:
>> Since commit 6b22b3d1614a ("kbuild: Allow using host dtc instead of
>> kernel's copy"), it is possible to use an external dtc.  In this
>> case, we do not know which options are supported on it.
>> 
>> Commit bc553986a2f7 ("dtc: turn off dtc unit address warnings by
>> default") gives -Wno-unit_address_vs_reg, but this options is only
>> recognized by v1.4.2 or later.
>> 
>> If an older version is specified, the build fails:
>
> But the option to use an external dtc was intended to allow testing of
> newer versions.  If there's no reason to use this option to run an
> older version, why bother trying to support that?

+1

That's a lot of added complexity, when the answer could just be "use the
kernel dtc".

cheers