Subject: Re: [PATCH 1/2] mtd/nand:Fix wrong address read in is_blank()

From: Prabhakar <[email-masked]>
Date: Wed, 4 Jan 2012 10:05:35 +0530

On Wednesday 04 January 2012 01:54 AM, Scott Wood wrote:
> On 12/28/2011 10:59 PM, Prabhakar Kushwaha wrote:
>> IFC NAND Machine calculates ECC on 512byte sector. Same is taken care in
>> fsl_ifc_run_command() while ECC status verification. Here buffer number is
>> calculated assuming 512byte sector and same is passed to is_blank.
>> However in is_blank() buffer address is calculated using mdt->writesize which is
>> wrong. It should be calculated on basis of ecc sector size.
>>
>> Also, in fsl_ifc_run_command() bufferpage is calculated on the basis of ecc sector
>> size instead of hard coded value.
>>
>> Signed-off-by: Poonam Aggrwal<[email-masked]>
>> Signed-off-by: Prabhakar Kushwaha<[email-masked]>
>> ---
>>   git://git.kernel.org/pub/scm/linux/kernel/git/galak/powerpc.git (branch next)
>>
>>   Tested on P1010RDB
>>
>>   drivers/mtd/nand/fsl_ifc_nand.c |    6 ++++--
>>   1 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mtd/nand/fsl_ifc_nand.c b/drivers/mtd/nand/fsl_ifc_nand.c
>> index 8475b88..2df7206 100644
>> --- a/drivers/mtd/nand/fsl_ifc_nand.c
>> +++ b/drivers/mtd/nand/fsl_ifc_nand.c
>> @@ -191,7 +191,9 @@ static int is_blank(struct mtd_info *mtd, unsigned int bufnum)
>>   {
>>   	struct nand_chip *chip = mtd->priv;
>>   	struct fsl_ifc_mtd *priv = chip->priv;
>> -	u8 __iomem *addr = priv->vbase + bufnum * (mtd->writesize * 2);
>> +	int bufperpage = mtd->writesize / chip->ecc.size;
>> +	u8 __iomem *addr = priv->vbase + bufnum / bufperpage
>> +					* (mtd->writesize * 2);
>>   	u32 __iomem *mainarea = (u32 *)addr;
>>   	u8 __iomem *oob = addr + mtd->writesize;
>>   	int i;
> This function should only be checking one ECC block, not the entire
> page.  The caller is responsible for passing in the appropriate buffer
> numbers.
>
> I think what the current code needs is for (mtd->writesize * 2) to be
> replaced with chip->ecc.size, and for the calling code to multiply the
> starting bufnum by two.

     Got your point :). I will take care in next patch version.

>> @@ -273,7 +275,7 @@ static void fsl_ifc_run_command(struct mtd_info *mtd)
>>   		dev_err(priv->dev, "NAND Flash Write Protect Error\n");
>>
>>   	if (nctrl->eccread) {
>> -		int bufperpage = mtd->writesize / 512;
>> +		int bufperpage = mtd->writesize / chip->ecc.size;
>>   		int bufnum = (nctrl->page&  priv->bufnum_mask) * bufperpage;
>>   		int bufnum_end = bufnum + bufperpage - 1;
>>
> Currently this driver always sets chip->ecc.size to 512.  If we want to
> support other ECC block sizes that future versions of IFC may have, can
> we calculate bufperpage during chip init (similar to bufnum_mask) to
> avoid the runtime division?  It's probably not huge overhead compared to
> everything else we do per NAND page transfer, but still...
>

   Yes. I agree.
    We are working on this in order to support new controller version.

--Prabhakar