linux-kernel - Re: [PATCH v2 3/3] Move IS_CONFIG

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Message-ID: <CAK7LNAS7sa6BdSjOZYUrTT3FaL_krD7JN8Cn_w7iLPfLAudUJA@mail.gmail.com>
Date:   Fri, 1 Oct 2021 11:33:11 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Lucas De Marchi <lucas.demarchi@...el.com>
Cc:     intel-gfx <intel-gfx@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] Move IS_CONFIG_NONZERO() to kconfig.h

On Fri, Oct 1, 2021 at 12:55 AM Lucas De Marchi
<lucas.demarchi@...el.com> wrote:
>
> On Thu, Sep 30, 2021 at 11:01:36PM +0900, Masahiro Yamada wrote:
> >On Thu, Sep 30, 2021 at 3:34 AM Lucas De Marchi
> ><lucas.demarchi@...el.com> wrote:
> >>
> >> The check for config value doesn't really belong to i915_utils.h - we
> >> are trying to eliminate that utils helper and share them when possible
> >> with other drivers and subsystems.
> >>
> >> Rationale for having such macro is in commit
> >> babaab2f4738 ("drm/i915: Encapsulate kconfig constant values inside boolean predicates")
> >> whereas later it is improved to not break the build if used with
> >> undefined configs. The caveat is detailed in the documentation: unlike
> >> IS_ENABLED(): it's not preprocessor-only logic so can't be used for
> >> things like `#if IS_CONFIG_NONZERO(...)`
> >>
> >> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
> >
> >
> >Hypothetical "it would be nice to have ..." is really unneeded.
> >
> >       if (context && CONFIG_DRM_I915_FENCE_TIMEOUT > 0)
> >                     return
> >msecs_to_jiffies_timeout(CONFIG_DRM_I915_FENCE_TIMEOUT);
> >
> >
> >is enough, and much cleaner.
> >
> >
> >
> >This warning is shown only when a constant is used
> >together with '&&'.
> >
> >Most of IS_ACTIVE can go away.
> >
> >Given that, there are not many places where the IS_ACTIVE macro
> >is useful, even in the i915 driver.
> >
> >For a few sources of the warnings,
> >replacing it with  != 0 or > 0 is just fine.
>
> humn... maybe. Let me do a conversion in that direction and see what is
> the outcome.
>
> My original intention was to make IS_ENABLED() even uglier to cover the
> int case, but after some tries it seems impossible to do on preprocessor
> context, so I thought maybe it would be ok as a separate one.
>
> >
> >Of course, such an ugly macro is not worth being moved to <linux/kconfig.h>
>
> if we don't handle the undefined case and only worry about encapsulating
> it inside a boolean predicate, the macro would be very simple. Would
> that be worth having in kconfig.h maybe?


I do not think so.

#define IS_CONFIG_NONZERO(config) ((config) != 0)

seems like a stupid macro.


What is bad about writing the direct code?

     if (x && CONFIG_FOO > 0)
                   ....





>
>
> thanks
> Lucas De Marchi



-- 
Best Regards
Masahiro Yamada