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

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Date:   Thu, 30 Sep 2021 23:01:36 +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 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.

Of course, such an ugly macro is not worth being moved to <linux/kconfig.h>




-- 
Best Regards
Masahiro Yamada