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

[Helmut Schaa]

On Thu, Dec 10, 2015 at 12:58 AM, Brian Norris
<computersforpeace at gmail.com> wrote:
> 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 at ti.com>
>> Cc: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>
>> Cc: David Woodhouse <David.Woodhouse at intel.com>
>> Signed-off-by: Helmut Schaa <helmut.schaa at 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?

I'm not carrying this patch in my tree anymore and did not see any more
crashes with the flash configuration I'm using. So, I think the original patch
is kind of superfluous.

Regards,
Helmut