linux-kernel - Re: [PATCH] drm/mediatek: hdmi: Perform NULL pointer check for mtk_hdmi

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Date:   Mon, 13 Dec 2021 21:08:15 +0800
From:   Chun-Kuang Hu <chunkuang.hu@...nel.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Collabora Kernel ML <kernel@...labora.com>
Subject: Re: [PATCH] drm/mediatek: hdmi: Perform NULL pointer check for mtk_hdmi_conf

 Hi, Angelo:

AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com> 於
2021年12月13日 週一 下午6:02寫道：
>
> Il 28/10/21 09:43, AngeloGioacchino Del Regno ha scritto:
> > In commit 41ca9caaae0b ("drm/mediatek: hdmi: Add check for CEA modes only")
> > a check for CEA modes was added to function mtk_hdmi_bridge_mode_valid()
> > in order to address possible issues on MT8167; moreover, with commit
> > c91026a938c2 ("drm/mediatek: hdmi: Add optional limit on maximal HDMI mode clock")
> > another similar check was introduced.
> >
> > Unfortunately though, at the time of writing, MT8173 does not provide
> > any mtk_hdmi_conf structure and this is crashing the kernel with NULL
> > pointer upon entering mtk_hdmi_bridge_mode_valid(), which happens as
> > soon as a HDMI cable gets plugged in.
> >
> > To fix this regression, add a NULL pointer check for hdmi->conf in the
> > said function, restoring HDMI functionality and avoiding NULL pointer
> > kernel panics.
> >
> > Fixes: 41ca9caaae0b ("drm/mediatek: hdmi: Add check for CEA modes only")
> > Fixes: c91026a938c2 ("drm/mediatek: hdmi: Add optional limit on maximal HDMI mode clock")
> > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> > ---
> >   drivers/gpu/drm/mediatek/mtk_hdmi.c | 12 +++++++-----
> >   1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
> > index 5838c44cbf6f..3196189429bc 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
> > @@ -1224,12 +1224,14 @@ static int mtk_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
> >                       return MODE_BAD;
> >       }
> >
> > -     if (hdmi->conf->cea_modes_only && !drm_match_cea_mode(mode))
> > -             return MODE_BAD;
> > +     if (hdmi->conf) {
> > +             if (hdmi->conf->cea_modes_only && !drm_match_cea_mode(mode))
> > +                     return MODE_BAD;
> >
> > -     if (hdmi->conf->max_mode_clock &&
> > -         mode->clock > hdmi->conf->max_mode_clock)
> > -             return MODE_CLOCK_HIGH;
> > +             if (hdmi->conf->max_mode_clock &&
> > +                 mode->clock > hdmi->conf->max_mode_clock)
> > +                     return MODE_CLOCK_HIGH;
> > +     }
> >
> >       if (mode->clock < 27000)
> >               return MODE_CLOCK_LOW;
> >
>
> Hello, friendly ping!
>
> Can I please get a review (or merge) of this commit?
>
> This is an important fix for a null pointer KP and restores HDMI functionality.

Applied to mediatek-drm-fixes [1], thanks.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/log/?h=mediatek-drm-fixes

Regards,
Chun-Kuang.

>
> Thanks,
> - Angelo