Re: [PATCH] mtd: nand: Do not automatically set SUBPAGE_READ flag

[Sascha Hauer <s.hauer@pengutronix.de>]

On Mon, Feb 24, 2014 at 10:20:05AM +0100, Hattink, Tjalling [FINT] wrote:
> > > The default nand_read_subpage implementation returns -ENOSUPP, so if
> > > you use a large nand chip without a specific read_subpage
> > > implementation the read operations will always fail.
> > >
> > > This functionaliy can be restored when a proper nand_read_subpage is
> > > implemented for the default driver.
> > >
> > > Signed-off-by: Tjalling Hattink <t.hattink@fugro.nl>
> > > ---
> > >  drivers/mtd/nand/nand_base.c | 4 ----
> > >  1 file changed, 4 deletions(-)
> > >
> > > diff --git a/drivers/mtd/nand/nand_base.c
> > > b/drivers/mtd/nand/nand_base.c index 54d8ba3..bfd695b 100644
> > > --- a/drivers/mtd/nand/nand_base.c
> > > +++ b/drivers/mtd/nand/nand_base.c
> > > @@ -3562,10 +3562,6 @@ int nand_scan_tail(struct mtd_info *mtd)
> > >         /* Invalidate the pagebuffer reference */
> > >         chip->pagebuf = -1;
> > >
> > > -       /* Large page NAND with SOFT_ECC should support subpage
> reads
> > */
> > > -       if ((chip->ecc.mode == NAND_ECC_SOFT) && (chip->page_shift >
> > 9))
> > > -               chip->options |= NAND_SUBPAGE_READ;
> > > -
> > 
> > Only barebox nand_read_subpage returns -ENOSUPP. The kernel has a
> > default implementation. Wouldn't it be possible (and better) to just
> > remove the return -ENOSUPP from nand_read_subpage and use the code
> > which we already have?
> > 
> > Sascha
> > 
> 
> Hi Sascha,
> 
> I will remove the ENOSUPP return code and compare the code with the
> kernel and test it. I'll publish a new patch if I have results (which is
> probably upcoming Friday).
> 
> I still wonder though why this -ENOSUPP return is added in the first
> place. The motivation written above it is somewhat unclear to me:
> "Currently we have no users in barebox, so disable this for now"

The motivation was to reduce the binary size. Should we remove the
-ENOSUPP it might be good thinking about the conditions under which we
need the code and add some Kconfig entry for it, or better use existing
ones if possible.

Sascha

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