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

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi Bean,

On Mon, 3 Apr 2017 11:31:05 +0000
"Bean Huo (beanhuo)" <beanhuo@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.

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

Regards,

Boris