[PATCH 4/5] mtd: nand: add support for Micron on-die ECC

[Bean Huo (beanhuo)]

>
>Hi Bean,
>
>On Mon, 3 Apr 2017 11:31:05 +0000
>"Bean Huo (beanhuo)" <beanhuo at micron.com> wrote:
>
>> Hi, Boris and Thomas
>>
>> >>
>> >> Ok, but I recommend that 70s should be the first choice on this
>> >> single solution, it doesn't need to read twice to detect its bitflips count.
>> >
>> >That's exactly why we need to differentiate the 2 chips.
>>
>> Sorry for later this response.
>> Below is the pseudo codes about how to differentiate these 2 series
>> parallel NAND with on-die ECC:
>>
>> if (NAND == SLC ) { // on-die ECC only exists in SLC //check device ID
>> byte 4
>>      if ((ID.byte4 & 0x02) == 0x02) {// internal ECC level ==10b
>
>So here the MT29F1G08ABADAWP datasheet says 0x2 <=> 4bit/512bytes ECC.
>
>> 	if (ID.byte4 & 0x80) {//on-Die ECC enabled
>
>Did you read my last reply?
>Thomas discovered that ID[4].bit7 is actually reflecting the ECC engine state (1 if
>the engine is enabled, 0 if it's disabled), not whether the NAND supports on-die
>ECC or not, so no this test is not reliable.
>
>>                     if (ONFI.byte112 == 4)
>> 		 60s SLC NAND with on-die ECC
>> 	    else if (ONFI.byte112 == 8)
>>      	              70s SLC NAND with on-die ECC
>
>This is completely fucked up! Now the ONFI param page says the NAND requires
>8bits/512bytes, while the ID bytes advertised an on-die ECC providing
>4bits/512bytes correctability.
>So either your algorithm is wrong, or the ID and ONFI param page are contracting
>(not sure what solution I'd prefer...).
>
>> 	    else
>>                           Doesn't support on-die ECC
>
>Sorry to say that, but I find it worrisome that even someone from Micron is not
>able to get it right.
>

Sorry, would you please specify which one is wrong or confuse you?

>I think we'll stick to the model name to detect whether on-die ECC is supported.
>
You want one solution that can clearly differentiate two serial SLC NAND, but NAND ONFI table
and device Id are always changing. It is easy to draw a perfect solution to do that.
OK, if you like maintain a huge/ugly table in MTD, please do that.

>Regards,
>
>Boris