[PATCH 3/3] nandtest: Introduce multiple reads & check iterations

Gupta, Pekon pekon at ti.com
Mon May 5 04:21:05 PDT 2014

Hi Artem,

>From: Artem Bityutskiy [mailto:dedekind1 at gmail.com]
>>On Mon, 2014-05-05 at 10:58 +0000, Gupta, Pekon wrote:
>> Therefore, I'm not sure having re-reads is a good test or not,
>> re-reads is changing the underlying testing scenario by introducing
>> _new_
>> bit-flips in neighboring regions pages because of read-disturbs.
>If the driver / HW cannot properly handle 4 re-reads, we do want the
>test to catch this, I think, irrespective of the true nature of the
>Therefore, I see this patch with a default 4 as an improvement.
>Best Regards,
>Artem Bityutskiy

I'm not against the patch, but my thought is that re-reads are
introducing read-disturb bit-flips.
Now in event of no UBIFS there would be no scrubbing. So these bit-flips
will keep on accumulating. And once these bit-flips cross beyond
ecc.strength then the nand_read is bound to fail.
So this makes this test un-deterministic.

Example: If I use this test with any driver using 1-bit ECC correction. Then
- test will most likely fail on weak or aged NAND devices, as they are more
  prone to read-disturb errors.
- But _may_ not fail on fresh devices using same driver with 1-bit ECC correction.

So my argument is that this test is actually not testing the NAND driver,
it is actually testing the weakness of NAND device.

with regards, pekon

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