AW: AW: NAND ECC errors

[Miquel Raynal]

On 08/08/2025 at 14:25:18 +02, <markus.stockhausen at gmx.de> wrote:

> Hi Miguel,
>
>> -----Ursprüngliche Nachricht-----
>> Von: Miquel Raynal <miquel.raynal at bootlin.com> 
>> Gesendet: Freitag, 8. August 2025 10:42
>>
>>
>> As explained in my other answer, you can now choose between ECC engines
>> when there are several. All happens at the SPI NAND level though, MTD,
>> UBI of filesystems are ignorant about it. They just expect (corrected)
>> data.
>>
>> However if your fw used to play with an external or pipelined ECC
>> engine, you are good to write a driver for it! But be happy, now there
>> is all the infrastructure needed for it.
>>
>> Reference implementations:
>> - drivers/mtd/nand/ecc-mxic.c
>> - drivers/mtd/nand/ecc-mtk.c
>
> Thanks a lot for your detailed explanations. The missing bit was the 
> info that all is in place for spi nand. I just was focused on that 
> on-die code snippet. So I was able to configure all I need. The DTS 
> reads now:
>
>   flash at 0 {
>     compatible = "spi-nand";
>     reg = <0>;
> 	
>     nand-use-soft-ecc-engine;
>     nand-ecc-algo = "bch";
>     nand-ecc-placement = "oob";
>     nand-ecc-strength = <6>;
>     nand-ecc-step-size = <512>;
>
> The software BCH engine is finally kicking in. Now there is a last
> small bit that is somehow off. As explained I found this data
>
> 4*512 bytes data
> 4*6 bytes (set to 0xff 0xff 0xff 0xff 0xff 0xff)
> 4*10 bytes ECC.
>
> While the bch6 code is automatically directed to the right ECC
> data slot the calculated checksums are totally different. So
> still unrecoverable errors. Looking deeper I noticed that the 
> original ECC was not only calculated over the 512 bytes data 
> but also over the 6*0xff extra bytes. These are simply appended.
>
> So we have
>
> DATA:
> 000 : 55 42 49 23 01 00 00 00 00 00 00 00 00 00 00 01 00 00 08 00 00 00 10 00 7b 6d c1 75 00 00 00 00
> 032 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 9f 21 e9 0b
> 064 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 096 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 128 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 160 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 192 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 224 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 256 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 288 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 320 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 352 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 384 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 416 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 448 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 480 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>
> ECC read from flash: a8 5e 66 15 61 32 de 2b 8b 44
> ECC BCH6 512 bytes : fa 7c bc 7b 44 c5 c7 b7 d8 6b
> ECC BCH6 518 (0xff): a8 5e 66 15 61 32 de 2b 8b 44
>
> This is consistent for all blocks. I'll add some hacks to
> software bch engine to verify it. Aside from the stupid
> idea of coding a bch "proxy" engine what would be a proper 
> solution?

Just to fully understand, you are trying to replicate what the software
BCH engine of your realtek SPI controller does?

If so, why not just configuring the engine directly and use it? It will
be much faster and easier to do.

Otherwise, if you're trying to do in software what the hardware does,
you must be prepared to more maths:
https://bootlin.com/blog/supporting-a-misbehaving-nand-ecc-engine/

Cheers,
Miquèl