linux-kernel - Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support large-page Nand chip

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Date:	Thu, 8 Dec 2011 18:44:54 +0800
From:	LiuShuo <b35362@...escale.com>
To:	Scott Wood <scottwood@...escale.com>
CC:	<shuo.liu@...escale.com>, <dwmw2@...radead.org>,
	<Artem.Bityutskiy@...ia.com>, <linux-mtd@...ts.infradead.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <leoli@...escale.com>
Subject: Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support
 large-page Nand chip

于 2011年12月08日 03:11, Scott Wood 写道:
> On 12/06/2011 09:55 PM, LiuShuo wrote:
>> 于 2011年12月07日 08:09, Scott Wood 写道:
>>> On 12/03/2011 10:31 PM, shuo.liu@...escale.com wrote:
>>>> From: Liu Shuo<shuo.liu@...escale.com>
>>>>
>>>> Freescale FCM controller has a 2K size limitation of buffer RAM. In
>>>> order
>>>> to support the Nand flash chip whose page size is larger than 2K bytes,
>>>> we read/write 2k data repeatedly by issuing FIR_OP_RB/FIR_OP_WB and save
>>>> them to a large buffer.
>>>>
>>>> Signed-off-by: Liu Shuo<shuo.liu@...escale.com>
>>>> ---
>>>> v3:
>>>>       -remove page_size of struct fsl_elbc_mtd.
>>>>       -do a oob write by NAND_CMD_RNDIN.
>>>>
>>>>    drivers/mtd/nand/fsl_elbc_nand.c |  243
>>>> ++++++++++++++++++++++++++++++++++----
>>>>    1 files changed, 218 insertions(+), 25 deletions(-)
>>> What is the plan for bad block marker migration?
>> This patch has been ported to uboot now, I think we can make a special
>> uboot image for bad
>> block marker migration when first use the chip.
> It should not be a special image, and there should be some way to mark
> that the migration has happened.  Even if we do the migration in U-Boot,
> Linux could check for the marker and if absent, disallow access and tell
> the user to run the migration tool.
>
>>>> @@ -473,13 +568,72 @@ static void fsl_elbc_cmdfunc(struct mtd_info
>>>> *mtd, unsigned int command,
>>>>             * write so the HW generates the ECC.
>>>>             */
>>>>            if (elbc_fcm_ctrl->oob || elbc_fcm_ctrl->column != 0 ||
>>>> -            elbc_fcm_ctrl->index != mtd->writesize + mtd->oobsize)
>>>> -            out_be32(&lbc->fbcr,
>>>> -                elbc_fcm_ctrl->index - elbc_fcm_ctrl->column);
>>>> -        else
>>>> +            elbc_fcm_ctrl->index != mtd->writesize + mtd->oobsize) {
>>>> +            if (elbc_fcm_ctrl->oob&&   mtd->writesize>   2048) {
>>>> +                out_be32(&lbc->fbcr, 64);
>>>> +            } else {
>>>> +                out_be32(&lbc->fbcr, elbc_fcm_ctrl->index
>>>> +                        - elbc_fcm_ctrl->column);
>>>> +            }
>>> We need to limit ourselves to the regions that have actually been
>>> written to in the buffer.  fbcr needs to be set separately for first and
>>> last subpages, with intermediate subpages having 0, 64, or 2112 as
>>> appropriate.  Subpages that are entirely before column or entirely after
>>> column + index should be skipped.
>> I have considered this case, but I don't think it is useful.
>>      1.There isn't a 'length' parameter in driver interface, although we
>> can get it from 'index - column'.
> Right.  column is start, and index is end + 1.  We have the bounds of
> what has been written.
>
>>      2.To see nand_do_write_oob() in nand_base.c, it fill '0xff' to
>> entire oob area first and write the user data by nand_fill_oob(), then
>> call ecc.write_oob (default is nand_write_oob_std()).
> Do we really want to assume that that's what it will always do?
>
> And if we do want to make such assumptions, we could rip out all usage
> of index/column here, and just handle "oob" and "full page" cases.
The function nand_do_write_ops() in nandbase.c is a Nand internal interface.
It always is called when application write to nand flash. (e.g. dd)
In this function, partial page write is dealt with by filling '0xff' to 
buffer before data copy.
(nand_do_write_oob() is similar)
So I don't think we need to do it in our controller driver again, it 
should be a job of upper layer.


I found that 'column' for NAND_CMD_SEQIN is always 0 or writesize except 
for oob write with
  NAND_ECC_HW_SYNDROME, but it's not useful case for our controller.

-LiuShuo
> -Scott


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