mtd: core: introduce of support for dynamic partitions

We have many parser that register mtd partitions at runtime. One example
is the cmdlinepart or the smem-part parser where the compatible is defined
in the dts and the partitions gets detected and registered by the
parser. This is problematic for the NVMEM subsystem that requires an OF
node to detect NVMEM cells.

To fix this problem, introduce an additional logic that will try to
assign an OF node to the MTD if declared.

On MTD addition, it will be checked if the MTD has an OF node and if
not declared will check if a partition with the same label / node name is
declared in DTS. If an exact match is found, the partition dynamically
allocated by the parser will have a connected OF node.

The NVMEM subsystem will detect the OF node and register any NVMEM cells
declared statically in the DTS.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220622010628.30414-4-ansuelsmth@gmail.com

Author: Ansuel

drivers/mtd/mtdcore.c

@@ -546,6 +546,66 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
 	return 0;
 }
 
+static void mtd_check_of_node(struct mtd_info *mtd)
+{
+	struct device_node *partitions, *parent_dn, *mtd_dn = NULL;
+	const char *pname, *prefix = "partition-";
+	int plen, mtd_name_len, offset, prefix_len;
+	struct mtd_info *parent;
+	bool found = false;
+
+	/* Check if MTD already has a device node */
+	if (dev_of_node(&mtd->dev))
+		return;
+
+	/* Check if a partitions node exist */
+	parent = mtd->parent;
+	parent_dn = dev_of_node(&parent->dev);
+	if (!parent_dn)
+		return;
+
+	partitions = of_get_child_by_name(parent_dn, "partitions");
+	if (!partitions)
+		goto exit_parent;
+
+	prefix_len = strlen(prefix);
+	mtd_name_len = strlen(mtd->name);
+
+	/* Search if a partition is defined with the same name */
+	for_each_child_of_node(partitions, mtd_dn) {
+		offset = 0;
+
+		/* Skip partition with no/wrong prefix */
+		if (!of_node_name_prefix(mtd_dn, "partition-"))
+			continue;
+
+		/* Label have priority. Check that first */
+		if (of_property_read_string(mtd_dn, "label", &pname)) {
+			of_property_read_string(mtd_dn, "name", &pname);
+			offset = prefix_len;
+		}
+
+		plen = strlen(pname) - offset;
+		if (plen == mtd_name_len &&
+		    !strncmp(mtd->name, pname + offset, plen)) {
+			found = true;
+			break;
+		}
+	}
+
+	if (!found)
+		goto exit_partitions;
+
+	/* Set of_node only for nvmem */
+	if (of_device_is_compatible(mtd_dn, "nvmem-cells"))
+		mtd_set_of_node(mtd, mtd_dn);
+
+exit_partitions:
+	of_node_put(partitions);
+exit_parent:
+	of_node_put(parent_dn);
+}
+
 /**
  *	add_mtd_device - register an MTD device
  *	@mtd: pointer to new MTD device info structure
@@ -658,6 +718,7 @@ int add_mtd_device(struct mtd_info *mtd)
 	mtd->dev.devt = MTD_DEVT(i);
 	dev_set_name(&mtd->dev, "mtd%d", i);
 	dev_set_drvdata(&mtd->dev, mtd);
+	mtd_check_of_node(mtd);
 	of_node_get(mtd_get_of_node(mtd));
 	error = device_register(&mtd->dev);
 	if (error)