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Date: Wed, 9 Dec 2015 15:58:23 -0800
From: Brian Norris <computersforpeace@gmail.com>
To: Helmut Schaa <helmut.schaa@googlemail.com>
Cc: linux-mtd@lists.infradead.org, David Woodhouse <David.Woodhouse@intel.com>,
 Artem Bityutskiy <artem.bityutskiy@linux.intel.com>,
 Pekon Gupta <pekon.gupta@gmail.com>
Subject: Re: [PATCH] mtd: nand: Disable subpage writes for drivers without
 ecc->hwctl
Message-ID: <20151209235823.GD144338@google.com>
References: <1397034804-27161-1-git-send-email-helmut.schaa@googlemail.com>
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Hi,

I have my archaeology hat on, in the deep corners of my mailbox...

On Wed, Apr 09, 2014 at 11:13:24AM +0200, Helmut Schaa wrote:
> nand_write_subpage_hwecc causes a crash if the driver did not register
> ecc->hwctl or ecc->calculate. Fix this by disabling subpage writes if
> ecc->hwctl or ecc->calculate is not provided by the driver.
> 
> This behavior was introduced in commit 837a6ba4f3b6d23026674e6af6b6849a4634fff9
> "mtd: nand: subpage write support for hardware based ECC schemes".
> 
> This fixes a crash with fsl_elbc_nand and maybe others:
> 
[...]
> 
> Cc: Gupta, Pekon <pekon@ti.com>
> Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
> Cc: David Woodhouse <David.Woodhouse@intel.com>
> Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
> ---
> I noticed this bug on openwrt with kernel 3.10 but it looks as if this can
> still happen in more recent kernels.
> 
>  drivers/mtd/nand/nand_base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index 9715a7b..2298289 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -3768,7 +3768,7 @@ int nand_scan_tail(struct mtd_info *mtd)
>  			ecc->write_oob = nand_write_oob_std;
>  		if (!ecc->read_subpage)
>  			ecc->read_subpage = nand_read_subpage;
> -		if (!ecc->write_subpage)
> +		if (!ecc->write_subpage && ecc->hwctl && ecc->calculate)
>  			ecc->write_subpage = nand_write_subpage_hwecc;
>  
>  	case NAND_ECC_HW_SYNDROME:

I realize we've merged a fix for fsl_elbc_nand long ago (commit
f034d87def51 "mtd: eLBC NAND: fix subpage write support"), but this
change still looks sane, applies, and could possibly fix some other
drivers that are lurking somewhere. Any reason I shouldn't apply it?

Regards,
Brian