mtd oob test is failing consistently at same places in NAND flash

[Ivan Djelic]

On Wed, May 09, 2012 at 04:12:05PM +0100, Philip, Avinash wrote:
> On Wed, May 09, 2012 at 00:15:16, Ivan Djelic wrote:
> > On Tue, May 08, 2012 at 04:09:46PM +0100, Philip, Avinash wrote:
> > > On Tue, May 08, 2012 at 18:53:54, Ivan Djelic wrote:
> > > > On Tue, May 08, 2012 at 01:33:06PM +0100, Philip, Avinash wrote:
> > > > > Hi,
> > > > > 
> > > > > We are having an 8-bit NAND part (MT29F2G08ABAEAWP from Micron) 
> > > > > connected to GPMC Module (General purpose memory controller) from TI.
> > > > 
> > > > Hi,
> > > > How is ecc performed ?
> > > > Using NAND internal ecc ? or with GPMC 1-bit Hamming ? 4-bit/8-bit BCH ?
> > > > Which version of omap2 driver are you using ?
> > > > Is OOB also ECC-protected ?
> > > 
> > > Hardware ECC is performing.
> > > 4-bit BCH ECC scheme is used.
> > > I am using omap2 driver in Linux 3.2.0 Kernel. Don't know omap2 driver version.
> > 
> > You are probably using a patched kernel, since 3.2.0 does not have GPMC BCH support ?!
> > What is your ecc layout ? Does it expose oobfree regions ?
> >
> 
> Yes, we had using patched kernel. OOB free region is exposed.
> 
> ECC layout will be as follows.
> 
> 0-1	-> BAD block marking
> 2-57  -> ECC byte position, ( 14 bytes for 512 byte)
> 58-63 -> oob free bytes
> 
> mtd->ecclayout->eccbytes		= 56
> mtd->ecclayout->eccpos[0]	= 2
> mtd->ecclayout->oobavail		= 6
> mtd->ecclayout->oobfree[0].offset	= 58
> mtd->ecclayout->oobfree[0].length	= 6
> 

OK, then it is quite normal that mtd_oobtest should fail when it encounters a
bitflip (one that does not match the programmed data) in those unprotected 6
bytes (58-63). What do you think ?

BR,
--
Ivan