Re: FAILED: patch "[PATCH] drm/mediatek: fix OF sibling-node lookup" failed to apply to 4.9-stable tree

[Johan Hovold <johan@kernel.org>]

On Wed, Nov 28, 2018 at 10:22:21AM -0500, Sasha Levin wrote:
> On Tue, Nov 27, 2018 at 07:16:56AM -0800, Johan Hovold wrote:
> >On Sun, Nov 11, 2018 at 08:17:40AM -0800, Greg Kroah-Hartman wrote:
> >>
> >> The patch below does not apply to the 4.9-stable tree.
> >> If someone wants it applied there, or to any other stable or longterm
> >> tree, then please email the backport, including the original git commit
> >> id to <stable@vger.kernel.org>.
> >
> >This one also depends on
> >
> >	36156f9241cb ("of: add helper to lookup compatible child node")
> 
> It seems to have more dependencies for 4.9.

Apparently just a trivial context change due to 4bf99144d2b4 ("drm:
Convert to using %pOF instead of full_name").

Compile-tested backport below.

Johan


>From 25904658b8a0975376a9118cfc07f5f3ebb1ea34 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Mon, 27 Aug 2018 10:21:46 +0200
Subject: [PATCH] drm/mediatek: fix OF sibling-node lookup

commit ceff2f4dcd44abf35864d9a99f85ac619e89a01d upstream.

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>
[ johan: backport to 4.9 ]
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/gpu/drm/mediatek/mtk_hdmi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
index e097780752f6..863d030786e5 100644
--- 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 %s\n",
 			cec_np->full_name);
+		of_node_put(cec_np);
 		return -EPROBE_DEFER;
 	}
+	of_node_put(cec_np);
 	hdmi->cec_dev = &cec_pdev->dev;
 
 	/*
-- 
2.19.2