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

[Chen-Yu Tsai]

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@xxxxxxxxxxxx>
Reviewed-by: Guillaume Ranquet <granquet@xxxxxxxxxxxx>
---
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