[PATCH 2/3] drm/mediatek: mtk_crtc: Skip the empty connector route slot in destroy

[zoan37 <agentzoan@gmail.com>]

A CRTC created with connector routes gets one extra ddp_comp[] slot for
its output component, and ddp_comp_nr counts it, but the slot stays
NULL until mtk_crtc_update_output() fills it in the first atomic
enable.

mtk_crtc_destroy() walks all ddp_comp_nr slots and passes each one to
mtk_ddp_comp_unregister_vblank_cb(), which dereferences it. Tearing
down a CRTC that was never enabled therefore dereferences NULL: unbinding
or removing mediatek-drm while that display path was never used, or
an error in mtk_drm_kms_init() after the CRTC was created.

Skip the empty slot. Nothing was registered for it anyway: the routed
components (DSI, DPI, DP_INTF, ...) have no vblank callback.

Fixes: 01389b324c97 ("drm/mediatek: Add connector dynamic selection capability")
Assisted-by: LLM
Signed-off-by: zoan37 <agentzoan@gmail.com>
---

Notes:
    Testing: found by reading the code; not reproduced. The same check runs
    on the MT8189 Chromebook described in patch 1 (boot, HDMI/DP hotplug,
    suspend/resume), but that does not exercise the destroy path (the
    driver is built in and was not unbound). Compile-tested (W=1) on
    next-20261008.

 drivers/gpu/drm/mediatek/mtk_crtc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
index b54f8565d2fa..704931b369b6 100644
--- a/drivers/gpu/drm/mediatek/mtk_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
@@ -145,6 +145,10 @@ static void mtk_crtc_destroy(struct drm_crtc *crtc)
 		struct mtk_ddp_comp *comp;
 
 		comp = mtk_crtc->ddp_comp[i];
+		/* The connector route slot is empty until the first enable */
+		if (!comp)
+			continue;
+
 		mtk_ddp_comp_unregister_vblank_cb(comp);
 	}
 
-- 
2.43.0