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

[Brian Norris <computersforpeace@gmail.com>]

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@gmail.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.

> 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

2. your patch is all white-space mangled. Please use your favorite
search engine to figure out how to get that right. git-send-email is
your friend.

Thanks,
Brian