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References: <20230202045734.2773503-1-wenst@chromium.org>
In-Reply-To: <20230202045734.2773503-1-wenst@chromium.org>
From:   Chun-Kuang Hu <chunkuang.hu@kernel.org>
Date:   Sun, 12 Mar 2023 23:41:31 +0800
Message-ID: <CAAOTY_8yhi2Vd01ph-W0HOmULs=tC5yARi_89Wddei=BTo5VKg@mail.gmail.com>
Subject: Re: [PATCH v2] drm/mediatek: dp: Only trigger DRM HPD events if
 bridge is attached
To:     Chen-Yu Tsai <wenst@chromium.org>
Cc:     Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel@lists.freedesktop.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org,
        Guillaume Ranquet <granquet@baylibre.com>
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Hi, Chen-Yu:

Chen-Yu Tsai <wenst@chromium.org> =E6=96=BC 2023=E5=B9=B42=E6=9C=882=E6=97=
=A5 =E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=8812:57=E5=AF=AB=E9=81=93=EF=BC=9A
>
> The MediaTek DisplayPort interface bridge driver starts its interrupts
> as soon as its probed. However when the interrupts trigger the bridge
> might not have been attached to a DRM device. As drm_helper_hpd_irq_event=
()
> does not check whether the passed in drm_device is valid or not, a NULL
> pointer passed in results in a kernel NULL pointer dereference in it.
>
> Check whether the bridge is attached and only trigger an HPD event if
> it is.

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

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/=
log/?h=3Dmediatek-drm-next

Regards,
Chun-Kuang.

>
> Fixes: f70ac097a2cf ("drm/mediatek: Add MT8195 Embedded DisplayPort drive=
r")
> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> Reviewed-by: Guillaume Ranquet <granquet@baylibre.com>
> ---
> Changes since v1
> - Dropped prerequisite-patch-ids
> - Added Guillaume's Reviewed-by
>
> This applies on top of mediatek-drm-next.
>
>  drivers/gpu/drm/mediatek/mtk_dp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek=
/mtk_dp.c
> index 1f94fcc144d3..a82f53e1a146 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
> @@ -1823,7 +1823,8 @@ static irqreturn_t mtk_dp_hpd_event_thread(int hpd,=
 void *dev)
>         spin_unlock_irqrestore(&mtk_dp->irq_thread_lock, flags);
>
>         if (status & MTK_DP_THREAD_CABLE_STATE_CHG) {
> -               drm_helper_hpd_irq_event(mtk_dp->bridge.dev);
> +               if (mtk_dp->bridge.dev)
> +                       drm_helper_hpd_irq_event(mtk_dp->bridge.dev);
>
>                 if (!mtk_dp->train_info.cable_plugged_in) {
>                         mtk_dp_disable_sdp_aui(mtk_dp);
> --
> 2.39.1.456.gfc5497dd1b-goog
>