drm/mediatek: fix OF sibling-node lookup

[ Upstream commit ceff2f4dcd44abf35864d9a99f85ac619e89a01d ]

Use the new of_get_compatible_child() helper to lookup the sibling
instead of using of_find_compatible_node(), which searches the entire
tree from a given start node and thus can return an unrelated (i.e.
non-sibling) node.

This also addresses a potential use-after-free (e.g. after probe
deferral) as the tree-wide helper drops a reference to its first
argument (i.e. the parent device node).

While at it, also fix the related cec-node reference leak.

Fixes: 8f83f26891e1 ("drm/mediatek: Add HDMI support")
Cc: stable <stable@vger.kernel.org>     # 4.8
Cc: Junzhi Zhao <junzhi.zhao@mediatek.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: CK Hu <ck.hu@mediatek.com>
Cc: David Airlie <airlied@linux.ie>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
index 690c675..aba27ea 100644 (file)
--- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
+++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
@@ -1446,8 +1446,7 @@ static int mtk_hdmi_dt_parse_pdata(struct mtk_hdmi *hdmi,
        }
 
        /* The CEC module handles HDMI hotplug detection */
-       cec_np = of_find_compatible_node(np->parent, NULL,
-                                        "mediatek,mt8173-cec");
+       cec_np = of_get_compatible_child(np->parent, "mediatek,mt8173-cec");
        if (!cec_np) {
                dev_err(dev, "Failed to find CEC node\n");
                return -EINVAL;
@@ -1457,8 +1456,10 @@ static int mtk_hdmi_dt_parse_pdata(struct mtk_hdmi *hdmi,
        if (!cec_pdev) {
                dev_err(hdmi->dev, "Waiting for CEC device %pOF\n",
                        cec_np);
+               of_node_put(cec_np);
                return -EPROBE_DEFER;
        }
+       of_node_put(cec_np);
        hdmi->cec_dev = &cec_pdev->dev;
 
        /*