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

From: Scott Wood <[email-masked]>
Date: Tue, 3 Jan 2012 14:24:02 -0600

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.

> @@ -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...

-Scott