From: Mason <slash.tmp@free.fr>
To: Pavel Machek <pavel@ucw.cz>,
Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Richard Weinberger <richard@nod.at>,
David Woodhouse <dwmw2@infradead.org>,
Brian Norris <computersforpeace@gmail.com>,
Marek Vasut <marek.vasut@gmail.com>,
Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
linux-mtd <linux-mtd@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
mark.marshall@omicronenergy.com, b44839@freescale.com,
prabhakar@freescale.com
Subject: Re: [PATCH] nand_base: optimize checking of erased buffers
Date: Wed, 17 May 2017 13:27:43 +0200 [thread overview]
Message-ID: <421c46b9-288f-42e9-5b2f-d93af1e8a418@free.fr> (raw)
In-Reply-To: <20170421105107.GA7259@amd>
On 21/04/2017 12:51, Pavel Machek wrote:
> 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));
I hadn't noticed this earlier. There is, obviously, an implicit
requirement that 'buf' must be 4-byte aligned on 32-bit platforms,
and 8-byte aligned on 64-bit platforms.
This is not true for my platform, as the ecc pointer is
chip->oob_poi + 10
I suppose it's not a problem if the platform can handle
unaligned loads, otherwise it spells trouble.
> + 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;
>
The optimization makes sense in itself, but given that it's on an
error path (?) I'm not sure it will bring any tangible benefits?
Regards.
next prev parent reply other threads:[~2017-05-17 11:28 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-19 12:13 fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek
2017-04-19 21:18 ` Boris Brezillon
2017-04-19 22:15 ` Pavel Machek
2017-04-19 22:27 ` Boris Brezillon
2017-04-20 11:40 ` Pavel Machek
2017-04-20 12:15 ` Boris Brezillon
2017-04-21 10:51 ` [PATCH] nand_base: optimize checking of erased buffers Pavel Machek
2017-05-17 11:27 ` Mason [this message]
2017-05-17 11:39 ` Mason
2017-05-17 11:52 ` Pavel Machek
2017-05-17 12:22 ` [PATCH] fsl_ifc_nand: fix handing of bit flips in erased nand Pavel Machek
2017-05-17 12:32 ` Boris Brezillon
2017-05-17 13:00 ` Pavel Machek
2017-05-17 13:25 ` Boris Brezillon
2017-05-17 20:03 ` [PATCH] mtd: nand: fsl_ifc: fix handing of bit flips in erased pages Pavel Machek
2017-05-31 20:59 ` [PATCHv2] " Pavel Machek
2017-05-31 22:59 ` Darwin Dingel
2017-06-01 1:09 ` Darwin Dingel
2017-06-01 13:12 ` Pavel Machek
2017-06-01 13:21 ` Boris Brezillon
2017-06-07 7:31 ` Boris Brezillon
2017-04-21 10:08 ` fsl_ifc_nand: are blank pages protected by ECC? Pavel Machek
2017-04-21 10:12 ` Richard Weinberger
2017-04-21 12:04 ` Boris Brezillon
2017-04-21 13:37 ` Pavel Machek
2017-04-21 13:49 ` Boris Brezillon
2017-04-22 7:01 ` Pavel Machek
2017-04-22 10:40 ` [PATCH] tango_nand.c: fix ecc.stats_corrected in empty flash case Pavel Machek
2017-04-23 9:58 ` tango_nand: is logic right in error cases? (was Re: fsl_ifc_nand: are blank pages protected by ECC?) Pavel Machek
2017-04-24 7:12 ` Boris Brezillon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=421c46b9-288f-42e9-5b2f-d93af1e8a418@free.fr \
--to=slash.tmp@free.fr \
--cc=b44839@freescale.com \
--cc=boris.brezillon@free-electrons.com \
--cc=computersforpeace@gmail.com \
--cc=cyrille.pitchen@wedev4u.fr \
--cc=dwmw2@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mtd@lists.infradead.org \
--cc=marek.vasut@gmail.com \
--cc=mark.marshall@omicronenergy.com \
--cc=pavel@ucw.cz \
--cc=prabhakar@freescale.com \
--cc=richard@nod.at \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).