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

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Date:   Thu,  2 Feb 2023 12:57:34 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Chen-Yu Tsai <wenst@...omium.org>, dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Guillaume Ranquet <granquet@...libre.com>
Subject: [PATCH v2] drm/mediatek: dp: Only trigger DRM HPD events if bridge is attached

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.

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