linux-kernel - Re: [PATCH] drm/edid: Fix EDID quirk compile error on older compilers

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Date:   Fri, 24 Sep 2021 14:58:32 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     dri-devel <dri-devel@...ts.freedesktop.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Srikanth Myakam <smyakam@...rosoft.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        LinusW <linus.walleij@...aro.org>,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/edid: Fix EDID quirk compile error on older compilers

Hi,

On Fri, Sep 24, 2021 at 7:53 AM Douglas Anderson <dianders@...omium.org> wrote:
>
> Apparently some compilers [1] cannot handle doing math on dereferenced
> string constants at compile time. This has led to reports [2] of
> compile errors like:
>
>   In file included from drivers/gpu/drm/drm_edid.c:42:0:
>   ./include/drm/drm_edid.h:525:2: error: initializer element is not constant
>     ((((u32)((vend)[0]) - '@') & 0x1f) << 26 | \
>
> Go back to the syntax I used in v4 of the patch series [3] that added
> this code instead of what landed (v5). This syntax is slightly uglier
> but should be much more compatible with varied compilers.
>
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69960#c18
> [2] https://lore.kernel.org/r/874kaabdt5.fsf@intel.com/
> [3] https://lore.kernel.org/r/20210909135838.v4.4.I6103ce2b16e5e5a842b14c7022a034712b434609@changeid/
>
> Fixes: d9f91a10c3e8 ("drm/edid: Allow querying/working with the panel ID from the EDID")
> Reported-by: Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>
> Reported-by: Srikanth Myakam <smyakam@...rosoft.com>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>  drivers/gpu/drm/drm_edid.c        | 121 +++++++++++++++---------------
>  drivers/gpu/drm/panel/panel-edp.c |  23 +++---
>  include/drm/drm_edid.h            |  14 ++--
>  3 files changed, 81 insertions(+), 77 deletions(-)

Landed in drm-misc-next:

7d1be0a09fa6 drm/edid: Fix EDID quirk compile error on older compilers