linux-kernel - Re: [PATCH 4/7] mtd: rawnand: sunxi: Fix ECC strength maximization

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Date:   Mon, 2 Jan 2023 10:11:32 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Brian Norris <computersforpeace@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 4/7] mtd: rawnand: sunxi: Fix ECC strength maximization

Hi Samuel,

samuel@...lland.org wrote on Thu, 29 Dec 2022 12:15:23 -0600:

> This is already accounted for in the subtraction for OOB, since the BBM
> overlaps the first OOB dword. With this change, the driver picks the
> same ECC strength as the vendor driver.
> 
> Fixes: 4796d8655915 ("mtd: nand: sunxi: Support ECC maximization")
> Signed-off-by: Samuel Holland <samuel@...lland.org>
> ---
> 
>  drivers/mtd/nand/raw/sunxi_nand.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
> index 1bddeb1be66f..1ecf2cee343b 100644
> --- a/drivers/mtd/nand/raw/sunxi_nand.c
> +++ b/drivers/mtd/nand/raw/sunxi_nand.c
> @@ -1643,8 +1643,7 @@ static int sunxi_nand_hw_ecc_ctrl_init(struct nand_chip *nand,
>  		ecc->size = 1024;
>  		nsectors = mtd->writesize / ecc->size;
>  
> -		/* Reserve 2 bytes for the BBM */
> -		bytes = (mtd->oobsize - 2) / nsectors;
> +		bytes = mtd->oobsize / nsectors;

I'm sorry but I don't think we can make this work. This change would
break all existing users...

>  
>  		/* 4 non-ECC bytes are added before each ECC bytes section */
>  		bytes -= 4;


Thanks,
Miquèl