linux-kernel - Re: [PATCH] Documentation: kbuild: explain handling optional dependencies

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Message-Id: <bc27450a-74cd-49f5-bc88-f102b0edb345@app.fastmail.com>
Date:   Fri, 15 Sep 2023 09:44:08 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Jani Nikula" <jani.nikula@...ux.intel.com>,
        "Masahiro Yamada" <masahiroy@...nel.org>
Cc:     "Arnd Bergmann" <arnd@...nel.org>,
        "Jonathan Corbet" <corbet@....net>,
        "Sakari Ailus" <sakari.ailus@....fi>,
        "Javier Martinez Canillas" <javierm@...hat.com>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Nicolas Schier" <nicolas@...sle.eu>, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Documentation: kbuild: explain handling optional dependencies

On Fri, Sep 15, 2023, at 09:34, Jani Nikula wrote:
>
> IS_REACHABLE() considered harmful.

Absolutely agreed, and I'm sorry I introduced it in the
first place in commit 9b174527e7b75 ("[media] Add and use
IS_REACHABLE macro").

At the time, it was only used by drivers/media, which used
to have a lot of open-coded instances of it and a lot of
wrong checks.

Having a formal syntax for it was an improvement for
drivers/media since it was more broken before, but it's
usually a mistake to use it when there is another solution,
and we probably should have tried harder to fix the
dependencies in drivers/media at the time.

      Arnd