Re: i.MX25 NFC with 8 bit ecc strength

[Baruch Siach <baruch@tkos.co.il>]

Hi Uwe,

On Tue, Apr 21, 2015 at 11:05:07AM +0200, Uwe Kleine-König wrote:
> On Tue, Apr 21, 2015 at 11:58:08AM +0300, Baruch Siach wrote:
> > On Tue, Apr 21, 2015 at 09:39:36AM +0200, Uwe Kleine-König wrote:
> > > While understanding the problem I produced the following (untested)
> > > patch:
> > > 
> > > diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
> > > index dca63a70e783..fc835d352e1c 100644
> > > --- a/drivers/mtd/nand/mxc_nand.c
> > > +++ b/drivers/mtd/nand/mxc_nand.c
> > > @@ -807,32 +807,49 @@ static void mxc_nand_select_chip_v2(struct mtd_info *mtd, int chip)
> > >  }
> > >  
> > >  /*
> > > - * Function to transfer data to/from spare area.
> > > + * The controller splits a page into data chunks of 512 bytes + partial oob.
> > > + * There are writesize / 512 such chunks, the size of the partial oob parts is
> > > + * oobsize / #chunks rounded down to a multiple of 2. The last oob chunk then
> > > + * contains additionally the byte lost by rounding (if any).
> > > + * This function handles the needed shuffling between host->data_buf (which
> > > + * holds a page in natural order, i.e. writesize bytes data + oobsize bytes
> > > + * spare) and the NFC buffer.
> > >   */
> > >  static void copy_spare(struct mtd_info *mtd, bool bfrom)
> > >  {
> > >  	struct nand_chip *this = mtd->priv;
> > >  	struct mxc_nand_host *host = this->priv;
> > >  	u16 i, j;
> > > -	u16 n = mtd->writesize >> 9;
> > > +
> > > +	u16 num_chunks = mtd->writesize / 512;
> > > +
> > >  	u8 *d = host->data_buf + mtd->writesize;
> > >  	u8 __iomem *s = host->spare0;
> > > -	u16 t = host->devtype_data->spare_len;
> > > +	u16 sparebuf_size = host->devtype_data->spare_len;
> > >  
> > > -	j = (mtd->oobsize / n >> 1) << 1;
> > > +	/* size of oob chunk for all but possibly the last one */
> > > +	oob_chunk_size = (mtd->oobsize / num_chunks >> 1) << 1;
> > >  
> > >  	if (bfrom) {
> > > -		for (i = 0; i < n - 1; i++)
> > > -			memcpy32_fromio(d + i * j, s + i * t, j);
> > > +		for (i = 0; i < num_chunks - 1; i++)
> > > +			memcpy32_fromio(d + i * oob_chunk_size,
> > > +					s + i * sparebuf_size,
> > > +					oob_chunk_size);
> > >  
> > >  		/* the last section */
> > > -		memcpy32_fromio(d + i * j, s + i * t, mtd->oobsize - i * j);
> > > +		memcpy32_fromio(d + i * oob_chunk_size,
> > > +				s + i * sparebuf_size,
> > > +				mtd->oobsize - i * oob_chunk_size);
> > >  	} else {
> > > -		for (i = 0; i < n - 1; i++)
> > > -			memcpy32_toio(&s[i * t], &d[i * j], j);
> > > +		for (i = 0; i < num_chunks - 1; i++)
> > > +			memcpy32_toio(&s[i * sparebuf_size],
> > > +				      &d[i * oob_chunk_size],
> > > +				      oob_chunk_size);
> > >  
> > >  		/* the last section */
> > > -		memcpy32_toio(&s[i * t], &d[i * j], mtd->oobsize - i * j);
> > > +		memcpy32_toio(&s[oob_chunk_size * sparebuf_size],
> > > +			      &d[i * oob_chunk_size],
> > > +			      mtd->oobsize - i * oob_chunk_size);
> > >  	}
> > >  }
> > > 
> > > What is needed now on top of this (untested and noop) change is to use
> > > the oob size the controller assumes instead of the real one and somehow
> > > explain that to the mtd layer and maintainers :-)
> > 
> > Can't we just limit oobsize to 128 or 218? Something like (on top of your 
> > patch):
> > 
> > diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
> > index cc0eb79a177c..ae63f06fe99e 100644
> > --- a/drivers/mtd/nand/mxc_nand.c
> > +++ b/drivers/mtd/nand/mxc_nand.c
> > @@ -819,7 +819,7 @@ static void copy_spare(struct mtd_info *mtd, bool bfrom)
> >  {
> >  	struct nand_chip *this = mtd->priv;
> >  	struct mxc_nand_host *host = this->priv;
> > -	u16 i, j;
> > +	u16 i, oob_chunk_size, used_oobsize;
> >  
> >  	u16 num_chunks = mtd->writesize / 512;
> >  
> > @@ -828,7 +828,13 @@ static void copy_spare(struct mtd_info *mtd, bool bfrom)
> >  	u16 sparebuf_size = host->devtype_data->spare_len;
> >  
> >  	/* size of oob chunk for all but possibly the last one */
> > -	oob_chunk_size = (mtd->oobsize / num_chunks >> 1) << 1;
> > +	if (mtd->oobsize >= 218)
> > +		used_oobsize = 218;
> > +	else if (mtd->oobsize >= 128)
> > +		used_oobsize = 128;
> > +	else
> > +		used_oobsize = mtd->oobsize;
> > +	oob_chunk_size = (used_oobsize / num_chunks >> 1) << 1;
> something like that, yes. I'd make that conditional on writesize=4k and
> the register setting that is actually used by the controler however.

Why? The 128/218 oob limit seems to apply to smaller pages as well, isn't it?

> Also you need to adapt the reading/setting of the last chunk to make use
> of used_oobsize instead of mtd->oobsize.

Right.

We also need a matching nand_ecclayout for 8 bit ecc.

baruch

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