[PATCH v5 3/4] mtd: Add get_mtd_device_by_node() helper

[Miquel Raynal <miquel.raynal@bootlin.com>]

From: Bernhard Frauendienst <kernel@nospam.obeliks.de>

Add an helper to retrieve a MTD device by its OF node. Since drivers can
assign arbitrary names to MTD devices in the absence of a 'label' DT
property, there is no other reliable way to retrieve a MTD device for a
given OF node.

Signed-off-by: Bernhard Frauendienst <kernel@nospam.obeliks.de>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
[<miquel.raynal@bootlin.com>: light internals rework]
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
---
 drivers/mtd/mtdcore.c   | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/mtd/mtd.h |  2 ++
 2 files changed, 40 insertions(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 76b4264936ff..5a94a2c0a6de 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -985,6 +985,44 @@ struct mtd_info *get_mtd_device_nm(const char *name)
 }
 EXPORT_SYMBOL_GPL(get_mtd_device_nm);
 
+/**
+ *	get_mtd_device_by_node - obtain a validated handle for an MTD device
+ *	by of_node
+ *	@of_node: OF node of MTD device to open
+ *
+ *	This function returns an MTD device structure in case of success,
+ *	an error code otherwise.
+ */
+struct mtd_info *get_mtd_device_by_node(const struct device_node *of_node)
+{
+	struct mtd_info *mtd;
+	bool found = false;
+	int ret;
+
+	mutex_lock(&mtd_table_mutex);
+
+	mtd_for_each_device(mtd) {
+		if (of_node == mtd->dev.of_node) {
+			found = true;
+			break;
+		}
+	}
+
+	if (found)
+		ret = __get_mtd_device(mtd);
+
+	mutex_unlock(&mtd_table_mutex);
+
+	if (!found)
+		return ERR_PTR(-ENODEV);
+
+	if (ret)
+		return ERR_PTR(ret);
+
+	return mtd;
+}
+EXPORT_SYMBOL_GPL(get_mtd_device_by_node);
+
 void put_mtd_device(struct mtd_info *mtd)
 {
 	mutex_lock(&mtd_table_mutex);
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 677768b21a1d..0f25c476a1a3 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -573,6 +573,8 @@ extern struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num);
 extern int __get_mtd_device(struct mtd_info *mtd);
 extern void __put_mtd_device(struct mtd_info *mtd);
 extern struct mtd_info *get_mtd_device_nm(const char *name);
+extern struct mtd_info *get_mtd_device_by_node(
+		const struct device_node *of_node);
 extern void put_mtd_device(struct mtd_info *mtd);
 
 
-- 
2.20.1