phy: tegra: fix device-tree node lookups

Fix child-node lookups during probe, which ended up searching the whole
device tree depth-first starting at the parents rather than just
matching on their children.

To make things worse, some parent nodes could end up being being
prematurely freed (by tegra_xusb_pad_register()) as
of_find_node_by_name() drops a reference to its first argument.

Fixes: 53d2a715 ("phy: Add Tegra XUSB pad controller support")
Cc: stable <stable@vger.kernel.org>     # 4.7
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

drivers/phy/tegra/xusb.c

@@ -75,14 +75,14 @@ MODULE_DEVICE_TABLE(of, tegra_xusb_padctl_of_match);
 static struct device_node *
 tegra_xusb_find_pad_node(struct tegra_xusb_padctl *padctl, const char *name)
 {
-	/*
-	 * of_find_node_by_name() drops a reference, so make sure to grab one.
-	 */
-	struct device_node *np = of_node_get(padctl->dev->of_node);
+	struct device_node *pads, *np;
 
-	np = of_find_node_by_name(np, "pads");
-	if (np)
-		np = of_find_node_by_name(np, name);
+	pads = of_get_child_by_name(padctl->dev->of_node, "pads");
+	if (!pads)
+		return NULL;
+
+	np = of_get_child_by_name(pads, name);
+	of_node_put(pads);
 
 	return np;
 }
@@ -90,16 +90,16 @@ tegra_xusb_find_pad_node(struct tegra_xusb_padctl *padctl, const char *name)
 static struct device_node *
 tegra_xusb_pad_find_phy_node(struct tegra_xusb_pad *pad, unsigned int index)
 {
-	/*
-	 * of_find_node_by_name() drops a reference, so make sure to grab one.
-	 */
-	struct device_node *np = of_node_get(pad->dev.of_node);
+	struct device_node *np, *lanes;
 
-	np = of_find_node_by_name(np, "lanes");
-	if (!np)
+	lanes = of_get_child_by_name(pad->dev.of_node, "lanes");
+	if (!lanes)
 		return NULL;
 
-	return of_find_node_by_name(np, pad->soc->lanes[index].name);
+	np = of_get_child_by_name(lanes, pad->soc->lanes[index].name);
+	of_node_put(lanes);
+
+	return np;
 }
 
 static int
@@ -195,7 +195,7 @@ int tegra_xusb_pad_register(struct tegra_xusb_pad *pad,
 	unsigned int i;
 	int err;
 
-	children = of_find_node_by_name(pad->dev.of_node, "lanes");
+	children = of_get_child_by_name(pad->dev.of_node, "lanes");
 	if (!children)
 		return -ENODEV;
 
@@ -444,21 +444,21 @@ static struct device_node *
 tegra_xusb_find_port_node(struct tegra_xusb_padctl *padctl, const char *type,
 			  unsigned int index)
 {
-	/*
-	 * of_find_node_by_name() drops a reference, so make sure to grab one.
-	 */
-	struct device_node *np = of_node_get(padctl->dev->of_node);
-
-	np = of_find_node_by_name(np, "ports");
-	if (np) {
+	struct device_node *ports, *np;
 	char *name;
 
+	ports = of_get_child_by_name(padctl->dev->of_node, "ports");
+	if (!ports)
+		return NULL;
+
 	name = kasprintf(GFP_KERNEL, "%s-%u", type, index);
-		if (!name)
+	if (!name) {
+		of_node_put(ports);
 		return ERR_PTR(-ENOMEM);
-		np = of_find_node_by_name(np, name);
-		kfree(name);
 	}
+	np = of_get_child_by_name(ports, name);
+	kfree(name);
+	of_node_put(ports);
 
 	return np;
 }
@@ -847,7 +847,7 @@ static void tegra_xusb_remove_ports(struct tegra_xusb_padctl *padctl)
 
 static int tegra_xusb_padctl_probe(struct platform_device *pdev)
 {
-	struct device_node *np = of_node_get(pdev->dev.of_node);
+	struct device_node *np = pdev->dev.of_node;
 	const struct tegra_xusb_padctl_soc *soc;
 	struct tegra_xusb_padctl *padctl;
 	const struct of_device_id *match;
@@ -855,7 +855,7 @@ static int tegra_xusb_padctl_probe(struct platform_device *pdev)
 	int err;
 
 	/* for backwards compatibility with old device trees */
-	np = of_find_node_by_name(np, "pads");
+	np = of_get_child_by_name(np, "pads");
 	if (!np) {
 		dev_warn(&pdev->dev, "deprecated DT, using legacy driver\n");
 		return tegra_xusb_padctl_legacy_probe(pdev);