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From: "Bean Huo (beanhuo)" <beanhuo@micron.com>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
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Subject: RE: [PATCH 4/5] mtd: nand: add support for Micron on-die ECC
Date: Tue, 11 Apr 2017 15:28:42 +0000
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Hi, Boris=20

>> Maybe I was wrong about your 'if ((ID.byte4 & 0x02) =3D=3D 0x02)' test,
>> because you apparently only mask bit 1 and not bits 0 and 1.

Sorry, here is my wrong, it should be masked with 0x3, not 0x02.=20

>> Anyway, I can't tell if this is valid because I don't have access to
>> the M79A datasheets you're referring to.
>
>Okay, I managed to download the MT29F2G08ABAGAWP datasheet (from the
>MT79A family), and it seems that the test should be
>
>	if ((ID.byte4 & 0x03) =3D=3D 0x02)
This is correct, should be 0x03, not 0x02.
>
>and not
>
>	if ((ID.byte4 & 0x02) =3D=3D 0x02)
>
>Also, this field named "Internal ECC level" clearly does not reflect the o=
n-die ECC
>strength because it's set to the same value on both parts (0x2) while
>MT29F2G08ABAGAWP provides 8bits/512bytes and MT29F1G08ABADAWP
>4bits/512bytes.
>
>See why I say we can't rely on READ_ID information. It's changing all the =
time,
>and nothing clearly say how to differentiate the scheme used in a specific=
 NAND
>part.

Correct, so far there is no standard to define ID.byte4, every vendor with =
their own definition.
Even with the same vendor, for the different products, this is also changin=
g.

Maintain one table in MTD, it is a simple and convenient way to differentia=
te, but, in my opinion,
This is not linux trend. We have method to automatically detect, why still =
maintain an additional table.