linux-kernel - Re: [PATCH 1/3] mtd: nand: Add on-die ECC support

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Message-ID: <20150428140347.GC2798@jcartwri.amer.corp.natinst.com>
Date:	Tue, 28 Apr 2015 09:03:47 -0500
From:	Josh Cartwright <joshc@...com>
To:	punnaiah choudary kalluri <punnaia@...inx.com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	Richard Weinberger <richard@....at>,
	Ben Shelton <ben.shelton@...com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Punnaiah Choudary Kalluri 
	<punnaiah.choudary.kalluri@...inx.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH 1/3] mtd: nand: Add on-die ECC support

On Tue, Apr 28, 2015 at 09:14:26AM +0530, punnaiah choudary kalluri wrote:
> On Tue, Apr 28, 2015 at 8:52 AM, Brian Norris <computersforpeace@...il.com> wrote:
> > On Tue, Apr 28, 2015 at 08:18:12AM +0530, punnaiah choudary kalluri wrote:
> >> On Tue, Apr 28, 2015 at 4:53 AM, Brian Norris <computersforpeace@...il.com> wrote:
[..]
> >> Agree that read_buf need not be returning raw data always including
> >> my new driver for arasan nand flash controller.
> >
> > I agree with that. At the moment, chip->read_buf() really has very
> > driver-specific meaning. Not sure if that's really a good thing, but
> > it's the way things are...
> >
> >> http://lkml.iu.edu/hypermail/linux/kernel/1504.2/00313.html
> >
> > In the half a minute I just spent looking at this (I may review it
> > properly later), I noted a few things:
> >
> > 1. you don't implement ecc.read_page_raw(); this means we'll probably
> > have trouble supporting on-die ECC with your driver, among other things
> 
> On-die ECC is optional as long as the controller has better ecc coverage.
> The arasan controller supports up to 24 bit ecc. There is no point to use
> on-die ECC and will always use hw ecc even for On-die ecc devices.

Maybe this is true of the controller instantiated in the Zynq MPSoC
chips, but the Zynq 7000 series SMC is documented to support only 1-bit
ECC.

(Which is why we're looking at your pl353 driver and this set).

  Josh

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