mtd: nand_bbt: use string library

Some nand_bbt code can be shortened by using memcmp() and memchr_inv().
As an added bonus, there is a possible performance benefit.

Borrowed some code from Akinobu Mita.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/nand_bbt.c

@@ -68,6 +68,7 @@
 #include <linux/delay.h>
 #include <linux/vmalloc.h>
 #include <linux/export.h>
+#include <linux/string.h>
 
 static int check_pattern_no_oob(uint8_t *buf, struct nand_bbt_descr *td)
 {
@@ -89,19 +90,16 @@ static int check_pattern_no_oob(uint8_t *buf, struct nand_bbt_descr *td)
  */
 static int check_pattern(uint8_t *buf, int len, int paglen, struct nand_bbt_descr *td)
 {
-	int i, end = 0;
+	int end = 0;
 	uint8_t *p = buf;
 
 	if (td->options & NAND_BBT_NO_OOB)
 		return check_pattern_no_oob(buf, td);
 
 	end = paglen + td->offs;
-	if (td->options & NAND_BBT_SCANEMPTY) {
-		for (i = 0; i < end; i++) {
-			if (p[i] != 0xff)
-				return -1;
-		}
-	}
+	if (td->options & NAND_BBT_SCANEMPTY)
+		if (memchr_inv(p, 0xff, end))
+			return -1;
 	p += end;
 
 	/* Compare the pattern */
@@ -111,10 +109,8 @@ static int check_pattern(uint8_t *buf, int len, int paglen, struct nand_bbt_desc
 	if (td->options & NAND_BBT_SCANEMPTY) {
 		p += td->len;
 		end += td->len;
-		for (i = end; i < len; i++) {
-			if (*p++ != 0xff)
-				return -1;
-		}
+		if (memchr_inv(p, 0xff, len - end))
+			return -1;
 	}
 	return 0;
 }
@@ -130,14 +126,9 @@ static int check_pattern(uint8_t *buf, int len, int paglen, struct nand_bbt_desc
  */
 static int check_short_pattern(uint8_t *buf, struct nand_bbt_descr *td)
 {
-	int i;
-	uint8_t *p = buf;
-
 	/* Compare the pattern */
-	for (i = 0; i < td->len; i++) {
-		if (p[td->offs + i] != td->pattern[i])
-			return -1;
-	}
+	if (memcmp(buf + td->offs, td->pattern, td->len))
+		return -1;
 	return 0;
 }