Re: [PATCH v2 1/4] dt-bindings: mtd: mtk-nand: Update properties description

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Mon, 16 Apr 2018 15:41:01 +0800
Xiaolei Li <xiaolei.li@mediatek.com> wrote:

> Update ecc step size, ecc strength, and parity bits supported on
> each MTK NAND controller.
> 
> Signed-off-by: Xiaolei Li <xiaolei.li@mediatek.com>
> ---
>  Documentation/devicetree/bindings/mtd/mtk-nand.txt | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/mtk-nand.txt b/Documentation/devicetree/bindings/mtd/mtk-nand.txt
> index 1c88526..ef786568 100644
> --- a/Documentation/devicetree/bindings/mtd/mtk-nand.txt
> +++ b/Documentation/devicetree/bindings/mtd/mtk-nand.txt
> @@ -50,14 +50,19 @@ Optional:
>  - nand-on-flash-bbt:	Store BBT on NAND Flash.
>  - nand-ecc-mode:	the NAND ecc mode (check driver for supported modes)
>  - nand-ecc-step-size:	Number of data bytes covered by a single ECC step.
> -			valid values: 512 and 1024.
> +			valid values:
> +			512 and 1024 on mt2701 and mt2712.
> +			512 only on mt7622.
>  			1024 is recommended for large page NANDs.
>  - nand-ecc-strength:	Number of bits to correct per ECC step.
> -			The valid values that the controller supports are: 4, 6,
> -			8, 10, 12, 14, 16, 18, 20, 22, 24, 28, 32, 36, 40, 44,
> -			48, 52, 56, 60.
> +			The valid values that each controller supports:
> +			mt2701: 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 28,
> +				32, 36, 40, 44, 48, 52, 56, 60.
> +			mt2712: 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 28,
> +				32, 36, 40, 44, 48, 52, 56, 60, 68, 72, 80.
> +			mt7622: 4, 6, 8, 10, 12, 14, 16.
>  			The strength should be calculated as follows:
> -			E = (S - F) * 8 / 14
> +			E = (S - F) * 8 / B
>  			S = O / (P / Q)
>  				E :	nand-ecc-strength.
>  				S :	spare size per sector.
> @@ -66,6 +71,9 @@ Optional:
>  				O :	oob size.
>  				P :	page size.
>  				Q :	nand-ecc-step-size.
> +				B :	parity bits to do 1 bit ECC.

Hm, this one is not clear. I guess what you wanted to say was "number
of parity bits needed to correct 1 bitflip". Even if what you say is
true, the value actually comes from the ECC step size, so I'm not
sure this is really useful to explain why it's 14 or 13 in the
dt-bindings doc.

> +					Be 14 on mt2701 and mt2712.
> +					Be 13 on mt7622.

					^ Should be

You can keep only that part.

>  			If the result does not match any one of the listed
>  			choices above, please select the smaller valid value from
>  			the list.