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

[Gupta, Pekon]

Hi Helmut Schaa,

>From: Helmut Schaa [mailto:helmut.schaa at googlemail.com]
>>Scott Wood <scottwood at freescale.com> schrieb:
[...]
>>> 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).
>
>Could be. I had to override the VID header offset accordingly to be able to attach to the ubi volume after applying this patch ...
>
There could be some misconfiguration in the way you generate your
UBIFS image. Just check following:
(1) min-io-size (-m) passed to mkfs.ubifs and ubinize commands?
(2) vid-hdr-offset (-O) passed to ubinize and ubiattach commands?
(3) subpage-size (-s) passed to ubinize commands? [optional]
All of the above should be set to $PAGE_SIZE of your NAND device.

Because if your image itself was generated such a way that vid-hdr was
offset at page-boundaries then you shouldn't have needed this change.
---------------------------
nand_base.c @@ nand_write_page(..)
	if (!(chip->options & NAND_NO_SUBPAGE_WRITE) &&
		chip->ecc.write_subpage)
		subpage = offset || (data_len < mtd->writesize);   <<-----
	else
		subpage = 0;
	[...]
	else if (subpage)  <<--------
		status = chip->ecc.write_subpage(mtd, chip, offset, data_len,
							 buf, oob_required);
---------------------------
So, even if the subpage-write is enabled, but all the write accesses are
page-aligned, (that is offset==0 && data_len % mtd->writesize ==0)
then also chip->ecc.write_subpage() does _not_ come in path.


with regards, pekon