[PATCH] mtd: nand: Added a device flag for subpage read support

[Jeff Westfahl]

Brian Norris <computersforpeace at gmail.com> wrote on 08/24/2012 07:05:45 
PM:

> From: Brian Norris <computersforpeace at gmail.com>
> To: dedekind1 at gmail.com
> Cc: Jeff Westfahl <jeff.westfahl at ni.com>, linux-mtd at lists.infradead.org
> Date: 08/24/2012 07:06 PM
> Subject: Re: [PATCH] mtd: nand: Added a device flag for subpage read 
support
> 
> On Fri, Aug 24, 2012 at 4:56 AM, Artem Bityutskiy <dedekind1 at gmail.com> 
wrote:
> > On Mon, 2012-08-13 at 16:35 -0500, Jeff Westfahl wrote:
> >> Added a NAND device flag for subpage read support. Previously this 
was
> >> hard coded based on large page and soft ECC.
> >> Updated base NAND driver to use the new subpage read flag if the NAND 
is
> >> large page and soft ECC.
> >>
> >> Signed-off-by: Jeff Westfahl <jeff.westfahl at ni.com>
> >
> > Brian, would you have a chance to review this patch?
> 
> Yes, I can try. I'll give it a little more thought on Monday.
> 
> But I have an initial question: why do you need this patch?
> Specifically, is there a driver you have that supports/needs this
> change? Right now, your new flag won't be used for anything new.
> 
> Side note: I have always thought that it was strange to have
> subpage-read support only baked into SOFT_ECC mode. There are
> presumably many potential applications in which a non-SOFT_ECC system
> could read partial pages safely.
> 
> Brian

Brian,

Your guess is correct. We're using an ARM SoC that isn't yet in mainline. 
Our
design is using NAND with on-die ECC. With on-die ECC enabled, partial 
pages
can be safely read. This patch helps cut UBI mount time on our board from
about 8 seconds to about 1 second.

Jeff