mtd: bcm47xxpart: alternative MAGIC for board_data partition

Some devices (like WNDR3700v3) have board_data without MPFR magic, some
extra header or extra NVRAM around 0x100. In such case we have to look
for another magic which is BD 0B 0D BD (BD probably stands for Board
Data). It's located "far far away", so instead of extending buffer add
another mtd_read.
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/bcm47xxpart.c

@@ -27,6 +27,7 @@
 
 /* Magics */
 #define BOARD_DATA_MAGIC		0x5246504D	/* MPFR */
+#define BOARD_DATA_MAGIC2		0xBD0D0BBD
 #define CFE_MAGIC			0x43464531	/* 1EFC */
 #define FACTORY_MAGIC			0x59544346	/* FCTY */
 #define POT_MAGIC1			0x54544f50	/* POTT */
@@ -192,6 +193,21 @@ static int bcm47xxpart_parse(struct mtd_info *master,
 					     offset, 0);
 			continue;
 		}
+
+		/* Read middle of the block */
+		if (mtd_read(master, offset + 0x8000, 0x4,
+			     &bytes_read, (uint8_t *)buf) < 0) {
+			pr_err("mtd_read error while parsing (offset: 0x%X)!\n",
+			       offset);
+			continue;
+		}
+
+		/* Some devices (ex. WNDR3700v3) don't have a standard 'MPFR' */
+		if (buf[0x000 / 4] == BOARD_DATA_MAGIC2) {
+			bcm47xxpart_add_part(&parts[curr_part++], "board_data",
+					     offset, MTD_WRITEABLE);
+			continue;
+		}
 	}
 
 	/* Look for NVRAM at the end of the last block. */