linux-kernel - Re: [PATCH 04/10] drm/print: Fix support for NULL as first argument of drm_dbg

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Message-ID: <21113999-99c2-0273-a6fe-8374ee910297@siddh.me>
Date:   Wed, 21 Dec 2022 21:05:34 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 04/10] drm/print: Fix support for NULL as first argument
 of drm_dbg_*

On Wed, Dec 21 2022 at 15:11:07 +0530, Jani Nikula wrote:
> On Wed, 21 Dec 2022, Siddh Raman Pant <code@...dh.me> wrote:
>> Comments say macros DRM_DEBUG_* are deprecated in favor of
>> drm_dbg_*(NULL, ...), but they have broken support for it,
>> as the macro will result in `(NULL) ? (NULL)->dev : NULL`.
> 
> What's wrong with that?

NULL is not a struct, so the syntax is incorrect.

Note that this isn't about a dev pointer whose value is
NULL, the first argument is NULL directly. So "NULL" is
directly substituted as is. If it was a dev pointer, then
the definition of struct allowed for no error, but here
gcc will generate the following error:

error: request for member ‘dev’ in something not a structure or union 

Hence, there is a need to fix them.

Thanks,
Siddh