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Subject[PATCH] nand_base: 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>

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index b0524f8..96c27ec 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1357,7 +1357,10 @@ 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;
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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