RE: [PATCH] Test for multi-bit error correction

[Artem Bityutskiy <dedekind1@gmail.com>]

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On Fri, 2012-08-31 at 08:59 +1000, Iwo Mergler wrote:
> This tests ECC biterror recovery on a single NAND page. Mostly intended
> to test ECC hardware and low-level NAND driver.
> 
> There are two test modes:
> 
>     0 - artificially inserting bit errors until the ECC fails
>         This is the default method and fairly quick. It should
>         be independent of the quality of the FLASH.
> 
>     1 - re-writing the same pattern repeatedly until the ECC fails.
>         This method relies on the physics of NAND FLASH to eventually
>         generate '0' bits if '1' has been written sufficient times. Depending
>         on the NAND, the first bit errors will appear after 1000 or
>         more writes and then will usually snowball, reaching the limits
>         of the ECC quickly.
> 
> The test stops after 10000 cycles, should your FLASH be exceptionally
> good and not generate bit errors before that. Try a different page
> offset in that case.
> 
> Please note that neither of these tests will significantly 'use up' any FLASH
> endurance. Only a maximum of two erase operations will be performed.
> 
> Signed-off-by: Iwo Mergler <Iwo.Mergler@netcommwireless.com.au>
> ---
>  drivers/mtd/tests/Makefile          |    1 +
>  drivers/mtd/tests/mtd_nandbiterrs.c |  460 +++++++++++++++++++++++++++++++++++
>  2 files changed, 461 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/mtd/tests/mtd_nandbiterrs.c
> 
> diff --git a/drivers/mtd/tests/Makefile b/drivers/mtd/tests/Makefile
> index b44dcab..bd0065c 100644
> --- a/drivers/mtd/tests/Makefile
> +++ b/drivers/mtd/tests/Makefile
> @@ -6,3 +6,4 @@ obj-$(CONFIG_MTD_TESTS) += mtd_stresstest.o
>  obj-$(CONFIG_MTD_TESTS) += mtd_subpagetest.o
>  obj-$(CONFIG_MTD_TESTS) += mtd_torturetest.o
>  obj-$(CONFIG_MTD_TESTS) += mtd_nandecctest.o
> +obj-$(CONFIG_MTD_TESTS) += mtd_nandbiterrs.o
> diff --git a/drivers/mtd/tests/mtd_nandbiterrs.c b/drivers/mtd/tests/mtd_nandbiterrs.c
> new file mode 100644
> index 0000000..94e908e
> --- /dev/null
> +++ b/drivers/mtd/tests/mtd_nandbiterrs.c
> @@ -0,0 +1,460 @@
> +/*
> + * (C)2012 NetCommWireless
> + * Iwo Mergler <Iwo.Mergler@netcommwireless.com.au>
> + *
> + * Test for multi-bit error recovery on a NAND page This mostly tests the
> + * ECC controller / driver.
> + *
> + * There are two test modes:
> + *
> + *	0 - artificially inserting bit errors until the ECC fails
> + *	    This is the default method and fairly quick. It should
> + *	    be independent of the quality of the FLASH.
> + *
> + *	1 - re-writing the same pattern repeatedly until the ECC fails.
> + *	    This method relies on the physics of NAND FLASH to eventually
> + *	    generate '0' bits if '1' has been written sufficient times.
> + *	    Depending on the NAND, the first bit errors will appear after
> + *	    1000 or more writes and then will usually snowball, reaching the
> + *	    limits of the ECC quickly.
> + *
> + *	    The test stops after 10000 cycles, should your FLASH be
> + *	    exceptionally good and not generate bit errors before that. Try
> + *	    a different page in that case.

So basically you test that ECC works, and you are trying to be
independent on the NAND HW and the ECC type. Right?

How about mtd_nandecc test? How is it different? Do we need 2 tests?
Why?

Akinobu - you recently sent a large patch-set for mtd_nandecctest, could
you please also comment on the above questions?

Basically, I would like to understand why we need 2 tests, and if we
really need 2, have the differences be documented, at least in the
commentaries.

-- 
Best Regards,
Artem Bityutskiy

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