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

[Scott Wood]

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).

-Scott