[PATCH] mtd: nand: Disable subpage writes for drivers without ecc->hwctl

[Scott Wood]

On Thu, 2014-04-10 at 04:19 +0000, Gupta, Pekon wrote:
> >From: Scott Wood [mailto:scottwood at freescale.com]
> >>On Wed, 2014-04-09 at 10:33 +0000, Gupta, Pekon wrote:
> >> >From: Helmut Schaa [mailto:helmut.schaa at googlemail.com]
> >> >>On Wed, Apr 9, 2014 at 11:38 AM, Gupta, Pekon <pekon at ti.com> wrote:
> >> [...]
> >> >>
> >> >> (1) if chip->ecc.hwctl() and chip->ecc.calculate are not implemented but you
> >> >>  still want to use subpage write feature, then you need to provide custom
> >> >>  implementation for chip->ecc.write_subpage().
> >> >>  that's same for other interfaces of nand_chip like chip->ecc.write_page().
> >> >
> >> >But these don't cause panics :)
> >> >
> >> because fsl_elbc_nand.c uses custom implementations of chip->ecc.write_page()
> >> 	@@ fsl_elbc_chip_init(...)
> >> 		chip->ecc.write_page = fsl_elbc_write_page;
> >>
> >> Same needs to be done if subpage write is needed. However, as this is
> >> a regression so please check if following patch solves your problem.[1]
> >>
> >>
> >> >> (2) If you don't want to use subpage write feature then just disable it using
> >> >>         chip->options |= NAND_NO_SUBPAGE_WRITE;
> >> >>
> >> >> Can you please tell which NAND controller driver is causing this ?
> >> >> We need to fix that..
> >> >
> >> >This happens with fsl_elbc_nand (while trying to run ubiformat on a
> >> >mtd dev) but the
> >> >crash was caused by the introduction of nand_write_subpage_hwecc. So, in this
> >> >case I think instead of trying to fix every possible driver we should
> >> >let the nand core
> >> >code handle this issue gracefully. Maybe we could add a WARN_ON_ONCE to
> >> >notice which drivers require adjustments.
> >> >
> >> Yes agree. May be good to keep subpage write disabled by default,
> >> as only handful drivers possibly use that.
> >>
> >>
> >> [1] ## <not compile tested>
> >> ------------
> >> From bfd39102ed6aa99b7ac2b8394a2d12b879fbb4b7 Mon Sep 17 00:00:00 2001
> >> From: Pekon Gupta <pekon at ti.com>
> >> Date: Wed, 9 Apr 2014 15:51:25 +0530
> >> Subject: [PATCH] mtd: eLBC NAND: disable subpage write support
> >>
> >> As fsl_elbc_nand do not implement NAND ECC interfaces (like chip->ecc.hwctl(),
> >> chip->ecc.calculate, and chip->ecc.correct) So it cannot use default
> >> implementation of nand_write_subpage_hwecc() as in nand_base.c.
> >> Hence disabling subpage write support till a custom implementation for
> >> chip->ecc_write_subpage is added.
> >>
> >> CC: <stable at vger.kernel.org> # 3.10.x+
> >> Signed-off-by: Pekon Gupta <pekon at ti.com>
> >> ---
> >>  drivers/mtd/nand/fsl_elbc_nand.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/mtd/nand/fsl_elbc_nand.c b/drivers/mtd/nand/fsl_elbc_nand.c
> >> index ec549cd..a21252c 100644
> >> --- a/drivers/mtd/nand/fsl_elbc_nand.c
> >> +++ b/drivers/mtd/nand/fsl_elbc_nand.c
> >> @@ -755,6 +755,7 @@ static int fsl_elbc_chip_init(struct fsl_elbc_mtd *priv)
> >>
> >>         /* set up nand options */
> >>         chip->bbt_options = NAND_BBT_USE_FLASH;
> >> +       chip->options |= NAND_NO_SUBPAGE_WRITE;
> >
> >Won't this break compatibility with existing UBI volumes?
> > That's why I didn't set this flag on eLBC when I set it on IFC (on the latter UBI is
> >simply broken without that flag, but eLBC gets away with it because of
> >the ECC algorithm used).
> 
> Are you sure subpage write is supported on this driver ? I couldn't find any
> custom implementation for chip->ecc.write_subpage() in fsl_elbc_nand.c.

I'm referring to UBI volumes created before chip->ecc.write_subpage()
existed.

-Scott