Re: fsl_ifc_nand: are blank pages protected by ECC?

Boris Brezillon
2017-04-20T12:16:03Z

On Thu, 20 Apr 2017 13:40:57 +0200
Pavel Machek <pavel@ucw.cz> wrote:

> 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.

Looks good to me. Can you send a patch with a real commit message?

Thanks,

Boris

>
> 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;
>