Re: fsl_ifc_nand: are blank pages protected by ECC?

From	Boris Brezillon <boris.brezillon@free-electrons.com>
Newsgroups	linux.kernel
Subject	Re: fsl_ifc_nand: are blank pages protected by ECC?
Date	2017-04-20 14:20 +0200
Message-ID	<tyje1-o7-1@gated-at.bofh.it> (permalink)
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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;
>

Thread

fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek <pavel@ucw.cz> - 2017-04-19 14:20 +0200
  Re: fsl_ifc_nand: are blank pages protected by ECC? Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-04-19 23:20 +0200
    Re: fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek <pavel@ucw.cz> - 2017-04-20 00:20 +0200
      Re: fsl_ifc_nand: are blank pages protected by ECC? Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-04-20 00:30 +0200
        Re: fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek <pavel@ucw.cz> - 2017-04-20 13:50 +0200
          Re: fsl_ifc_nand: are blank pages protected by ECC? Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-04-20 14:20 +0200
          [PATCH] nand_base: optimize checking of erased buffers Pavel Machek <pavel@ucw.cz> - 2017-04-21 13:00 +0200
    Re: fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek <pavel@ucw.cz> - 2017-04-21 12:10 +0200
      Re: fsl_ifc_nand: are blank pages protected by ECC? Richard Weinberger <richard@nod.at> - 2017-04-21 12:20 +0200
      Re: fsl_ifc_nand: are blank pages protected by ECC? Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-04-21 14:10 +0200
      Re: fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek <pavel@ucw.cz> - 2017-04-21 15:40 +0200
        Re: fsl_ifc_nand: are blank pages protected by ECC? Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-04-21 15:50 +0200
          Re: fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek <pavel@ucw.cz> - 2017-04-22 09:10 +0200
          [PATCH] tango_nand.c: fix ecc.stats_corrected in empty flash case Pavel Machek <pavel@ucw.cz> - 2017-04-22 12:50 +0200
          tango_nand: is logic right in error cases? (was Re: fsl_ifc_nand:  are blank pages protected by ECC?) Pavel Machek <pavel@ucw.cz> - 2017-04-23 12:00 +0200
            Re: tango_nand: is logic right in error cases? (was Re:  fsl_ifc_nand: are blank pages protected by ECC?) Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-04-24 09:20 +0200

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