linux-kernel - Re: [PATCH 1/2] if_enabled.h: Add IF_ENABLED_OR_ELSE() and IF

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Date:   Wed, 09 Dec 2020 11:31:41 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Arnd Bergmann <arnd@...nel.org>, od@...c.me,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] if_enabled.h: Add IF_ENABLED_OR_ELSE()
 and
 IF_ENABLED() macros

Hi Linus,

Le mer. 9 déc. 2020 à 9:59, Linus Walleij <linus.walleij@...aro.org> 
a écrit :
> On Tue, Dec 8, 2020 at 5:48 PM Paul Cercueil <paul@...pouillou.net> 
> wrote:
> 
>>  Introduce a new header <linux/if_enabled.h>, that brings two new 
>> macros:
>>  IF_ENABLED_OR_ELSE() and IF_ENABLED().
> 
> I understand what the patch is trying to do, but when we already have
> IS_ENABLED() in <linux/kconfig.h> this syntax becomes a big cognitive
> confusion for the mind.
> 
> At least the commit needs to explain why it doesn't work to use
> IS_ENABLED() instead so that this is needed.

You can use IS_ENABLED(). Then you'd write:

field = IS_ENABLED(CONFIG_FOO) ? &my_ptr : NULL,

the IF_ENABLED() macro makes it a bit cleaner by allowing you to write:

field = IF_ENABLED(CONFIG_FOO, &my_ptr),

Cheers,
-Paul

> Certainly the build failures must be possible to solve so that this
> can live with the sibling IS_ENABLED() inside <linux/kconfig.h>,
> it can't be too hard.
> 
> Yours,
> Linus Walleij