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Date: Mon, 20 Apr 2020 10:53:13 -0300
From: Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword
Message-ID: <20200420135313.GN26002@ziepe.ca>
References: <20200417011146.83973-1-saeedm@mellanox.com>
 <CAK7LNAQZd_LUyA2V_pCvMTr_201nSX1Nm0TDw5kOeNV64rOfpA@mail.gmail.com>
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Sender: linux-kbuild-owner@vger.kernel.org
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To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Saeed Mahameed <saeedm@mellanox.com>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Nicolas Pitre <nico@fluxnic.net>, Jani Nikula <jani.nikula@linux.intel.com>, Neil Armstrong <narmstrong@baylibre.com>, Laurent Pinchart <Laurent.pinchart@ideasonboard.com>, Leon Romanovsky <leon@kernel.org>, Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>, jonas@kwiboo.se, David Airlie <airlied@linux.ie>, jernej.skrabec@siol.net, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Networking <netdev@vger.kernel.org>, linux-rdma@vger.kernel.org

On Sun, Apr 19, 2020 at 04:00:43AM +0900, Masahiro Yamada wrote:

> People would wonder, "what 'uses FOO' means?",
> then they would find the explanation in kconfig-language.rst:
> 
>   "Equivalent to: depends on symbol || !symbol
>   Semantically it means, if FOO is enabled (y/m) and has the option:
>   uses BAR, make sure it can reach/use BAR when possible."
> 
> To understand this correctly, people must study
> the arithmetic of (symbol || !symbol) anyway.

I think people will just cargo-cult copy it and not think too hard
about how kconfig works.

The descriptions in kconfig-language.rst can be improved to better
guide C people using kconfig without entirely understanding
it. Something like:

 BAR depends on FOO // BAR selects FOO: BAR requires functionality from
 FOO

 BAR uses FOO: BAR optionally consumes functionality from FOO using
 IS_ENABLED

 BAR implies FOO: BAR optionally consumes functionality from FOO using
 IS_REACHABLE

Now someone adding IS_ENABLED or IS_REACHABLE checks to C code knows
exactly what to put in the kconfig.

Jason