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 ed08e39..79d98c9 100644 (file)
--- 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;