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

[Philip, Avinash]

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.
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
>