From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Matthias Auchmann <m.auchmann@artech.at>
Cc: Richard Weinberger <richard@nod.at>,
"linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
Brian Norris <computersforpeace@gmail.com>,
Sascha Hauer <s.hauer@pengutronix.de>
Subject: Re: mtd locking
Date: Mon, 30 May 2016 11:24:16 +0200 [thread overview]
Message-ID: <20160530112416.73e8a875@bbrezillon> (raw)
In-Reply-To: <574B15FE.8030206@nod.at>
+Brian and Sasha
Hi Matthias,
On Sun, 29 May 2016 18:17:02 +0200
Richard Weinberger <richard@nod.at> wrote:
> Hi!
>
> Am 29.05.2016 um 17:53 schrieb Matthias Auchmann:
> > By intended you mean it's wrong and we know, but it's still wrong, right?
>
> I'd say lazy. Sometimes counters don't need to be exact.
> Having exact counting is expensive. See network stack.
>
> I'm not sure what the exact reasons in the ECC error counting
> case are.
> Maybe Brian or Boris can tell more.
>
> > What about thread safety in general? Is the rest of the mtd system thread safe? Can it happen that e.g. a command is issued to NAND, and before the buffer is read, another command is issued (and similar scenarios)? Or is there some kind of protection in place for that?
>
> NAND chip access is strictly serialized. :-)
> See nand_get_device().
Yep, read/write accesses are correctly protected. The statistics update
are also protected, but it does not prevent tools like nanddump to
retrieve incorrect information. Actually, nanddump uses the following
sequence:
1/ get stats
2/ read stuff
3/ get new stats and compare with information retrieved in #1
Since we can't lock access to the MTD device for the whole sequence,
the statistics might change because of other read accesses on the same
MTD device.
I recently suggested the addition of a new ioctl to address that [1].
Regards,
Boris
[1]http://thread.gmane.org/gmane.linux.drivers.mtd/66834
--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
next prev parent reply other threads:[~2016-05-30 9:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-29 13:38 mtd locking Matthias Auchmann
2016-05-29 14:23 ` Richard Weinberger
2016-05-29 15:53 ` Matthias Auchmann
2016-05-29 16:17 ` Richard Weinberger
2016-05-30 9:24 ` Boris Brezillon [this message]
2016-05-31 18:11 ` Brian Norris
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