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

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Message-ID: <20210930155547.rtz6pdae42gqvm6p@ldmartin-desk2>
Date:   Thu, 30 Sep 2021 08:55:47 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
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 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?


thanks
Lucas De Marchi