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

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Message-ID: <CAGnW=BaBFKZc+hrTFg+YYf_aN7=Oj2QkC07raAgKJGGbW99UmQ@mail.gmail.com>
Date:	Tue, 28 Apr 2015 21:49:51 +0530
From:	punnaiah choudary kalluri <punnaia@...inx.com>
To:	Josh Cartwright <joshc@...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 7:33 PM, Josh Cartwright <joshc@...com> wrote:
> 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.

True. SMC controller in zynq supports only 1 -bit ECC. One can use
on-die ECC devices
and turn of the controller ECC for better ECC coverage. I am also
exploring the options
to use these patches with the pl353 driver in a  generic way and
acceptable to all.

Regards,
Punnaiah
>
> (Which is why we're looking at your pl353 driver and this set).
>
>   Josh
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