linux-kernel - Re: [PATCH v2] drm/mediatek: dp: Only trigger DRM HPD events if bridge is attached

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Date:   Sun, 12 Mar 2023 23:41:31 +0800
From:   Chun-Kuang Hu <chunkuang.hu@...nel.org>
To:     Chen-Yu Tsai <wenst@...omium.org>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Guillaume Ranquet <granquet@...libre.com>
Subject: Re: [PATCH v2] drm/mediatek: dp: Only trigger DRM HPD events if
 bridge is attached

Hi, Chen-Yu:

Chen-Yu Tsai <wenst@...omium.org> 於 2023年2月2日 週四 下午12:57寫道：
>
> 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=mediatek-drm-next

Regards,
Chun-Kuang.

>
> Fixes: f70ac097a2cf ("drm/mediatek: Add MT8195 Embedded DisplayPort driver")
> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> Reviewed-by: Guillaume Ranquet <granquet@...libre.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
>