mtd: bcm63xxpart: Extract read of image tag to separate function

Extract image tag reading and CRC check to a separate function.
Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/bcm63xxpart.c

@@ -41,6 +41,10 @@
 #define BCM963XX_CFE_VERSION_OFFSET	0x570
 #define BCM963XX_NVRAM_OFFSET		0x580
 
+/* Ensure strings read from flash structs are null terminated */
+#define STR_NULL_TERMINATE(x) \
+	do { char *_str = (x); _str[sizeof(x) - 1] = 0; } while (0)
+
 static int bcm63xx_detect_cfe(struct mtd_info *master)
 {
 	char buf[9];
@@ -89,6 +93,37 @@ static int bcm63xx_read_nvram(struct mtd_info *master,
 	return 0;
 }
 
+static int bcm63xx_read_image_tag(struct mtd_info *master, const char *name,
+	loff_t tag_offset, struct bcm_tag *buf)
+{
+	int ret;
+	size_t retlen;
+	u32 computed_crc;
+
+	ret = mtd_read(master, tag_offset, sizeof(*buf), &retlen, (void *)buf);
+	if (ret)
+		return ret;
+
+	if (retlen != sizeof(*buf))
+		return -EIO;
+
+	computed_crc = crc32_le(IMAGETAG_CRC_START, (u8 *)buf,
+				offsetof(struct bcm_tag, header_crc));
+	if (computed_crc == buf->header_crc) {
+		STR_NULL_TERMINATE(buf->board_id);
+		STR_NULL_TERMINATE(buf->tag_version);
+
+		pr_info("%s: CFE image tag found at 0x%llx with version %s, board type %s\n",
+			name, tag_offset, buf->tag_version, buf->board_id);
+
+		return 0;
+	}
+
+	pr_warn("%s: CFE image tag at 0x%llx CRC invalid (expected %08x, actual %08x)\n",
+		name, tag_offset, buf->header_crc, computed_crc);
+	return 1;
+}
+
 static int bcm63xx_parse_cfe_partitions(struct mtd_info *master,
 					const struct mtd_partition **pparts,
 					struct mtd_part_parser_data *data)
@@ -99,13 +134,11 @@ static int bcm63xx_parse_cfe_partitions(struct mtd_info *master,
 	struct bcm_tag *buf = NULL;
 	struct mtd_partition *parts;
 	int ret;
-	size_t retlen;
 	unsigned int rootfsaddr, kerneladdr, spareaddr;
 	unsigned int rootfslen, kernellen, sparelen, totallen;
 	unsigned int cfelen, nvramlen;
 	unsigned int cfe_erasesize;
 	int i;
-	u32 computed_crc;
 	bool rootfs_first = false;
 
 	if (bcm63xx_detect_cfe(master))
@@ -134,28 +167,13 @@ static int bcm63xx_parse_cfe_partitions(struct mtd_info *master,
 	}
 
 	/* Get the tag */
-	ret = mtd_read(master, cfelen, sizeof(struct bcm_tag), &retlen,
-		       (void *)buf);
-
-	if (retlen != sizeof(struct bcm_tag)) {
-		ret = -EIO;
-		goto out;
-	}
-
-	computed_crc = crc32_le(IMAGETAG_CRC_START, (u8 *)buf,
-				offsetof(struct bcm_tag, header_crc));
-	if (computed_crc == buf->header_crc) {
-		char *boardid = &(buf->board_id[0]);
-		char *tagversion = &(buf->tag_version[0]);
-
+	ret = bcm63xx_read_image_tag(master, "rootfs", cfelen, buf);
+	if (!ret) {
 		sscanf(buf->flash_image_start, "%u", &rootfsaddr);
 		sscanf(buf->kernel_address, "%u", &kerneladdr);
 		sscanf(buf->kernel_length, "%u", &kernellen);
 		sscanf(buf->total_length, "%u", &totallen);
 
-		pr_info("CFE boot tag found with version %s and board type %s\n",
-			tagversion, boardid);
-
 		kerneladdr = kerneladdr - BCM963XX_EXTENDED_SIZE;
 		rootfsaddr = rootfsaddr - BCM963XX_EXTENDED_SIZE;
 		spareaddr = roundup(totallen, master->erasesize) + cfelen;
@@ -169,13 +187,13 @@ static int bcm63xx_parse_cfe_partitions(struct mtd_info *master,
 			rootfsaddr = kerneladdr + kernellen;
 			rootfslen = spareaddr - rootfsaddr;
 		}
-	} else {
-		pr_warn("CFE boot tag CRC invalid (expected %08x, actual %08x)\n",
-			buf->header_crc, computed_crc);
+	} else if (ret > 0) {
 		kernellen = 0;
 		rootfslen = 0;
 		rootfsaddr = 0;
 		spareaddr = cfelen;
+	} else {
+		goto out;
 	}
 	sparelen = master->size - spareaddr - nvramlen;