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

[Philip, Avinash]

On Tue, May 08, 2012 at 20:39:46, 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.

One correction, 8-bit BCH ECC scheme used,

> I am using omap2 driver in Linux 3.2.0 Kernel. Don't know omap2 driver version.
> No, OOB is not ECC protected.
> 
> > 
> > > We have been seeing mtd_oobtest failure on a partition size of 248 MB. 
> > > Most of the time, test case 2 of mtd_oobtest is failing. On 
> > > debugging further it seems that bit flip is happening on the test 
> > > case 2 in OOB area. It is observed that the failure locations are consistent.
> > 
> > If you are able to reproduce failures, then you should be able to tell which bits in OOB are failing, by adding a few debugging lines in the code.
> > 
> 
> I add debugs and found bit flips from 1 to 0. The location of bit flips might vary on boards. But on the same board it is consistent.
> 
> > > To verify further we had tried writing zeros to OOB area and read it back. 
> > > This test is passing and confirms that all OOB bits (that are
> > > programmable) are not bad.
> > 
> > It does not confirm anything, bits can fail by remaining stuck at 0.
> >
> 
> As bit flip is from 1 to 0, you are right. But same experiment with 0x55, test is passing.
>  
> > BR,
> > --
> > Ivan
> > 
> 
> 
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