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Date:   Mon, 2 Sep 2019 00:42:56 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Palmer Dabbelt <palmer@sifive.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-riscv@lists.infradead.org
Subject: Re: [PATCH] riscv: add arch/riscv/Kbuild
Message-ID: <20190902074256.GA754@infradead.org>
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On Sat, Aug 31, 2019 at 10:04:53PM +0900, Masahiro Yamada wrote:
> Kbuild support two file names, "Makefile" and "Kbuild"
> for describing obj-y, obj-m, etc.

<snipping the basic explanation, which is documented pretty well,
I I think I full understand>

> Similarly, arch/$(SRCARCH)/Makefile is very special
> in that it is included from the top-level Makefile,
> and specify arch-specific compiler flags etc.
> 
> We can use arch/$(SRCARCH)/Kbuild
> to specify obj-y, obj-m.
> The top-level Makefile does not need to know
> the directory structure under arch/$(SRCARCH)/.
> 
> This is logical separation.

But only if we document this specific split and eventually stop allowing 
to build objects from arch/$(SRCARCH)/Makefile.  And in my perfect world
we'd eventually phase out the magic arch/$(SRCARCH)/Makefile entireŀy.
In addition to the normal Kbuild file we'd then have say (names entirely
made up and probably not the best idea)

  arch/$(SRCARCH)/flags.mk to set the various compiler flags and co
  arch/$(SRCARCH)/targets.mk for extra arch-specific targets