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

[Bean Huo (beanhuo)]

Hi, Boris and Thomas
Let me do some explanation.

>> 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 the NAND supports on-die ECC, here should be 10b, not matter it is 8bit or 4bit,
You are correct, MT29F1G08ABADAWP is 0x2, its explanation is 4bit/512bytes ECC.
But for the 70s, it is 8bit on-die ECC, but it is still 10b. 
So that why here using these two bits to determine if exist on-die ECC.
What's more, for some old products, they don't support on-die ECC,
Sometimes, here is still 01b, so still need following codes to do further
determinations.

>> 	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.
>
For the on-die ECC, it is not always default enabled. It depends on requirement from costumers.
If on-die ECC is not enabled, bit7 is 0. It can be switched through "Feature Operations".

>>                     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.

I think, my previous answers can answer this confusion.

>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.
>
I am ashamed. I have been in Micron for two years, for some old products, I am also not very clear.
But I checked all the SLC-NAND datasheet with on-die ECC with our AE, and had this final pseudo code.

>I think we'll stick to the model name to detect whether on-die ECC is supported.
>
>Regards,
>
>Boris

beanhuo