mtd: allow getting MTD device associated with a specific DT node

MTD subsystem API allows interacting with MTD devices (e.g. reading,
writing, handling bad blocks). So far a random driver could get MTD
device only by its name (get_mtd_device_nm()). This change allows
getting them also by a DT node.

This API is required for drivers handling DT defined MTD partitions in a
specific way (e.g. U-Boot (sub)partition with environment variables).
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20220916122100.170016-3-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mtd/mtdcore.c

@@ -1217,6 +1217,34 @@ int __get_mtd_device(struct mtd_info *mtd)
 }
 EXPORT_SYMBOL_GPL(__get_mtd_device);
 
+/**
+ * of_get_mtd_device_by_node - obtain an MTD device associated with a given node
+ *
+ * @np: device tree node
+ */
+struct mtd_info *of_get_mtd_device_by_node(struct device_node *np)
+{
+	struct mtd_info *mtd = NULL;
+	struct mtd_info *tmp;
+	int err;
+
+	mutex_lock(&mtd_table_mutex);
+
+	err = -EPROBE_DEFER;
+	mtd_for_each_device(tmp) {
+		if (mtd_get_of_node(tmp) == np) {
+			mtd = tmp;
+			err = __get_mtd_device(mtd);
+			break;
+		}
+	}
+
+	mutex_unlock(&mtd_table_mutex);
+
+	return err ? ERR_PTR(err) : mtd;
+}
+EXPORT_SYMBOL_GPL(of_get_mtd_device_by_node);
+
 /**
  *	get_mtd_device_nm - obtain a validated handle for an MTD device by
  *	device name

include/linux/mtd/mtd.h

@@ -677,6 +677,7 @@ extern int mtd_device_unregister(struct mtd_info *master);
 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 *of_get_mtd_device_by_node(struct device_node *np);
 extern struct mtd_info *get_mtd_device_nm(const char *name);
 extern void put_mtd_device(struct mtd_info *mtd);