linux-kernel - [PATCH 1/3] of: always populate a root node

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Date:   Wed, 27 Apr 2022 11:45:00 +0200
From:   Clément Léger <clement.leger@...tlin.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Clément Léger <clement.leger@...tlin.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazonni@...tlin.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Andrew Lunn <andrew@...n.ch>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Rob Herring <robh@...nel.org>
Subject: [PATCH 1/3] of: always populate a root node

When enabling CONFIG_OF on a platform where of_root is not populated by
firmware, we end up without a root node. In order to apply overlays and
create subnodes of the root node, we need one. This commit creates an
empty root node if not present.

Co-developed-by: Rob Herring <robh@...nel.org>
Signed-off-by: Rob Herring <robh@...nel.org>
Signed-off-by: Clément Léger <clement.leger@...tlin.com>
---
 drivers/of/base.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index e7d92b67cb8a..6b8584c39f73 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -177,6 +177,19 @@ void __init of_core_init(void)
 		pr_err("failed to register existing nodes\n");
 		return;
 	}
+
+	if (!of_root) {
+		of_root = kzalloc(sizeof(*of_root), GFP_KERNEL);
+		if (!of_root) {
+			mutex_unlock(&of_mutex);
+			pr_err("failed to create root node\n");
+			return;
+		}
+
+		of_root->full_name = "/";
+		of_node_init(of_root);
+	}
+
 	for_each_of_allnodes(np) {
 		__of_attach_node_sysfs(np);
 		if (np->phandle && !phandle_cache[of_phandle_cache_hash(np->phandle)])
@@ -185,8 +198,7 @@ void __init of_core_init(void)
 	mutex_unlock(&of_mutex);
 
 	/* Symlink in /proc as required by userspace ABI */
-	if (of_root)
-		proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
+	proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
 }
 
 static struct property *__of_find_property(const struct device_node *np,
-- 
2.34.1