The WRT1900AC among other Linksys routers uses a dual-firmware layout.
The bootloader passes the active rootfs in bootargs and also sets the
rootfstype to jffs2 - which is clearly something we don't want.

Rename both root= and rootfstype= variables to avoid issues and also
use the former to dynamically rename the active partition to "ubi".


Signed-off-by: Imre Kaloz <kaloz@openwrt.org>

--- a/arch/arm/boot/compressed/atags_to_fdt.c
+++ b/arch/arm/boot/compressed/atags_to_fdt.c
@@ -66,6 +66,18 @@ static uint32_t get_cell_size(const void
 	return cell_size;
 }
 
+static void mangle_bootargs(void *fdt, const char *fdt_cmdline)
+{
+	char *rootdev;
+	char *rootfs;
+
+	rootdev = strstr(fdt_cmdline, "root=/dev/mtdblock");
+	strncpy(rootdev, "uboot_active_root=", 18);
+
+	rootfs = strstr(fdt_cmdline, "rootfstype");
+	strncpy(rootfs, "origfstype", 10);
+}
+
 static void merge_fdt_bootargs(void *fdt, const char *fdt_cmdline)
 {
 	char cmdline[COMMAND_LINE_SIZE];
@@ -135,6 +147,9 @@ int atags_to_fdt(void *atag_list, void *
 
 	for_each_tag(atag, atag_list) {
 		if (atag->hdr.tag == ATAG_CMDLINE) {
+			/* Rename the original root= and rootfstype= options */
+			mangle_bootargs(fdt,
+					   atag->u.cmdline.cmdline);
 			/* Append the ATAGS command line to the device tree
 			 * command line.
 			 * NB: This means that if the same parameter is set in
--- a/arch/arm/boot/compressed/string.c
+++ b/arch/arm/boot/compressed/string.c
@@ -111,6 +111,53 @@ char *strchr(const char *s, int c)
 	return (char *)s;
 }
 
+/**
+ * strncpy - Copy a length-limited, %NUL-terminated string
+ * @dest: Where to copy the string to
+ * @src: Where to copy the string from
+ * @count: The maximum number of bytes to copy
+ *
+ * The result is not %NUL-terminated if the source exceeds
+ * @count bytes.
+ *
+ * In the case where the length of @src is less than  that  of
+ * count, the remainder of @dest will be padded with %NUL.
+ *
+ */
+char *strncpy(char *dest, const char *src, size_t count)
+{
+	char *tmp = dest;
+
+	while (count) {
+		if ((*tmp = *src) != 0)
+			src++;
+		tmp++;
+		count--;
+	}
+	return dest;
+}
+
+/**
+ * strstr - Find the first substring in a %NUL terminated string
+ * @s1: The string to be searched
+ * @s2: The string to search for
+ */
+char *strstr(const char *s1, const char *s2)
+{
+	size_t l1, l2;
+
+	l2 = strlen(s2);
+	if (!l2)
+		return (char *)s1;
+	l1 = strlen(s1);
+	while (l1 >= l2) {
+		l1--;
+		if (!memcmp(s1, s2, l2))
+			return (char *)s1;
+		s1++;
+	}
+	return NULL;
+}
 #undef memset
 
 void *memset(void *s, int c, size_t count)
--- a/drivers/mtd/ofpart.c
+++ b/drivers/mtd/ofpart.c
@@ -25,12 +25,15 @@ static bool node_has_compatible(struct d
 	return of_get_property(pp, "compatible", NULL);
 }
 
+static int uboot_active_root;
+
 static int parse_ofpart_partitions(struct mtd_info *master,
 				   struct mtd_partition **pparts,
 				   struct mtd_part_parser_data *data)
 {
 	struct device_node *node;
 	const char *partname;
+	const char *owrtpart = "ubi";
 	struct device_node *pp;
 	int nr_parts, i;
 
@@ -78,9 +81,15 @@ static int parse_ofpart_partitions(struc
 		(*pparts)[i].offset = of_read_number(reg, a_cells);
 		(*pparts)[i].size = of_read_number(reg + a_cells, s_cells);
 
-		partname = of_get_property(pp, "label", &len);
-		if (!partname)
-			partname = of_get_property(pp, "name", &len);
+		if (uboot_active_root && (i == uboot_active_root)) {
+				partname = owrtpart;
+		} else {
+			partname = of_get_property(pp, "label", &len);
+
+			if (!partname)
+				partname = of_get_property(pp, "name", &len);
+		}
+
 		(*pparts)[i].name = partname;
 
 		if (of_get_property(pp, "read-only", &len))
@@ -178,6 +187,18 @@ static int __init ofpart_parser_init(voi
 	return 0;
 }
 
+static int __init active_root(char *str)
+{
+	get_option(&str, &uboot_active_root);
+
+	if (!uboot_active_root)
+		return 1;
+
+	return 1;
+}
+
+__setup("uboot_active_root=", active_root);
+
 static void __exit ofpart_parser_exit(void)
 {
 	deregister_mtd_parser(&ofpart_parser);
