From: Pavel Machek <pavel@ucw.cz>
Date: Fri, 21 Apr 2017 10:51:07 +0000 (+0200)
Subject: mtd: nand: Optimize checking of erased buffers
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=086567f12e1188c57e061a53825a5eff5a7923a0;p=linux.git

mtd: nand: Optimize checking of erased buffers

If we see ~0UL in flash, there's no need for hweight, and no need to
check number of bitflips. So this should be net win.

Signed-off-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
---

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index ed08e3946727e..79d98c9fa8a75 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1421,7 +1421,10 @@ static int nand_check_erased_buf(void *buf, int len, int bitflips_threshold)
 
 	for (; len >= sizeof(long);
 	     len -= sizeof(long), bitmap += sizeof(long)) {
-		weight = hweight_long(*((unsigned long *)bitmap));
+		unsigned long d = *((unsigned long *)bitmap);
+		if (d == ~0UL)
+			continue;
+		weight = hweight_long(d);
 		bitflips += BITS_PER_LONG - weight;
 		if (unlikely(bitflips > bitflips_threshold))
 			return -EBADMSG;