linux-kernel - Re: [PATCH] drm/amd/display: Fix an uninitialized index variable

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Date:   Thu, 25 Feb 2021 23:08:23 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nathan Chancellor <nathan@...nel.org>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        Stylon Wang <stylon.wang@....com>,
        Eryk Brol <eryk.brol@....com>,
        Bas Nieuwenhuizen <bas@...nieuwenhuizen.nl>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Simon Ser <contact@...rsion.fr>,
        Qingqing Zhuo <qingqing.zhuo@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] drm/amd/display: Fix an uninitialized index variable

On Thu, Feb 25, 2021 at 10:34 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
> return parse_edid_cea(aconnector, edid_ext, EDID_LENGTH, vsdb_info) ? i : -ENODEV;
>
> would suffice, but the patch is still fine as is.

Right, I did not want to change more than necessary here, and the
original code already had the extra assignment instead of returning
the value.

> > @@ -9857,8 +9857,8 @@ void amdgpu_dm_update_freesync_caps(struct drm_connector *connector,
> >                         }
> >                 }
> >         } else if (edid && amdgpu_dm_connector->dc_sink->sink_signal == SIGNAL_TYPE_HDMI_TYPE_A) {
> > -               hdmi_valid_vsdb_found = parse_hdmi_amd_vsdb(amdgpu_dm_connector, edid, &vsdb_info);
> > -               if (hdmi_valid_vsdb_found && vsdb_info.freesync_supported) {
> > +               i = parse_hdmi_amd_vsdb(amdgpu_dm_connector, edid, &vsdb_info);
> > +               if (i >= 0 && vsdb_info.freesync_supported) {
>
> reusing `i` here is safe, for now, but reuse of variables like this in
> separate branches like this might not get noticed if the function is
> amended in the future.
>
> >                         timing  = &edid->detailed_timings[i];
> >                         data    = &timing->data.other_data;

The entire point of the patch is that 'i' is in fact used in the following line,
but was lacking an intialization.

       Arnd