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

[Philip, Avinash]

Hi,

We are having an 8-bit NAND part (MT29F2G08ABAEAWP from Micron) connected to GPMC
Module (General purpose memory controller) from TI.
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. 

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.

To test further I had modified the mtd_oobtest.c as follows and found this
test is passing

diff --git a/drivers/mtd/tests/mtd_oobtest.c b/drivers/mtd/tests/mtd_oobtest.c
index 933f7e5..9f118de 100644
--- a/drivers/mtd/tests/mtd_oobtest.c
+++ b/drivers/mtd/tests/mtd_oobtest.c
@@ -50,7 +50,7 @@ static unsigned long next = 1;

static inline unsigned int simple_rand(void)
{
-       next = next * 1103515245 + 12345;
+       next = next * 1103515244 + 12345; /* 45 -> 44. Sequence is changed */
        return (unsigned int)((next / 65536) % 32768);
}


Is this behavior due to bits getting corrupted on certain sequence? 
Is this issue observed by anyone else?

Thanks & Regards
Avinash Philip