Re: fsl_ifc_nand: are blank pages protected by ECC?

Pavel Machek
2017-04-20T11:41:08Z

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Hi!

> > Would it make sense to only do hweight if *bitmap != ~0ULL ? Would it
> > make sense to only check for bitflips > bitflips_threshold each 128
> > bytes or something like that?
>
> I didn't go as far as you did and simply assumed hweight32/64() were
> already optimized. Feel free to propose extra improvements.

I'd propose this one (only compile tested, sorry, not sure how to test
this one). If we see ~0UL, 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;