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

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Date:	Fri, 8 May 2015 14:39:47 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Ben Shelton <ben.shelton@...com>
Cc:	punnaiah choudary kalluri <punnaia@...inx.com>,
	Richard Weinberger <richard@....at>,
	"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 Fri, May 08, 2015 at 04:26:32PM -0500, Ben Shelton wrote:
> On 04/27, Brian Norris 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:
> > > > On Tue, Apr 28, 2015 at 12:19:16AM +0200, Richard Weinberger wrote:
> > > >> Oh, I thought every driver has to implement that function. ;-\
> > > >
> > > > Nope.
> > > >
> > > >> But you're right there is a corner case.
> > > >
> > > > And it's not the only one! Right now, there's no guarantee even that
> > > > read_buf() returns raw data, unmodified by the SoC's controller. Plenty
> > > > of drivers actually have HW-enabled ECC turned on by default, and so
> > > > they override the chip->ecc.read_page() (and sometimes
> > > > chip->ecc.read_page_raw() functions, if we're lucky) with something
> > > > that pokes the appropriate hardware instead. I expect anything
> > > > comprehensive here is probably going to have to utilize
> > > > chip->ecc.read_page_raw(), at least if it's provided by the hardware
> > > > driver.
> > > 
> > > Yes, overriding the chip->ecc.read_page_raw would solve this.
> > 
> > I'm actually suggesting that (in this patch set, for on-die ECC
> > support), maybe we *shouldn't* override chip->ecc.read_page_raw() and
> > leave that to be defined by the driver, and then on-die ECC support
> > should be added in a way that just calls chip->ecc.read_page_raw(). This
> > should work for any driver that already properly supports the raw
> > callbacks.
> > 
> 
> Hi Richard et al,
> 
> I'm guessing it's probably too late for the on-die ECC stuff to land in
> 4.2 at this point.

Not technically. We've got several weeks (approx 5 to 6?) before 4.1 is
released. 4.2 material should be getting finalized by a week or so
before the merge window (i.e., 4 to 5 weeks from now).

> Is there anything I can do to help this along
> (testing, etc.)?

This is going to need to get rewritten. I'm not sure if Richard is going
to tackle this again, as he hasn't responded to the points I brought up.
(Note that Richard is not the first to have tried to implement this,
without initial success.)

Brian
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