Re: [PATCH] mtd: rawnand: sunxi: reject invalid ECC step sizes

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: James Hilliard <james.hilliard1@gmail.com>
Cc: linux-mtd@lists.infradead.org,  linux-sunxi@lists.linux.dev,
	stable@vger.kernel.org,  Richard Weinberger <richard@nod.at>,
	 Vignesh Raghavendra <vigneshr@ti.com>,
	 Chen-Yu Tsai <wens@kernel.org>,
	 Jernej Skrabec <jernej.skrabec@gmail.com>,
	 Samuel Holland <samuel@sholland.org>,
	Richard Genoud <richard.genoud@bootlin.com>,
	 Geert Uytterhoeven <geert+renesas@glider.be>,
	 Boris Brezillon <bbrezillon@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mtd: rawnand: sunxi: reject invalid ECC step sizes
Date: Fri, 04 Sep 2026 17:25:28 +0200	[thread overview]
Message-ID: <87ecf911jr.fsf@bootlin.com> (raw)
In-Reply-To: <20260811060651.227431-1-james.hilliard1@gmail.com> (James Hilliard's message of "Tue, 11 Aug 2026 00:06:48 -0600")

On 11/08/2026 at 00:06:48 -06, James Hilliard <james.hilliard1@gmail.com> wrote:

> ECC maximization forces a 1024-byte ECC step and divides the
> available OOB bytes by the number of steps. A NAND with a smaller
> page therefore produces zero steps and a division by zero.

No, steps cannot be < 1. If they are, it's a bug that must be fixed.

> An explicitly configured ECC step which is larger than, or does not
> divide, the page also produces an unusable step count before the NAND
> core can diagnose the configuration.
>
> Validate the step size at both points where the driver derives the
> number of sectors and reject invalid geometries.
>
> Fixes: 4796d8655915 ("mtd: nand: sunxi: Support ECC maximization")
> Cc: stable@vger.kernel.org
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
>  drivers/mtd/nand/raw/sunxi_nand.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
> index 45ccbce91551..ad314c0e30b2 100644
> --- a/drivers/mtd/nand/raw/sunxi_nand.c
> +++ b/drivers/mtd/nand/raw/sunxi_nand.c
> @@ -2032,6 +2032,15 @@ static void sunxi_nand_detach_chip(struct nand_chip *nand)
>  	sunxi_nand->user_data_bytes = NULL;
>  }
>  
> +static int sunxi_nfc_ecc_steps(struct mtd_info *mtd, unsigned int step_size)
> +{
> +	if (!step_size || mtd->writesize < step_size ||
> +	    mtd->writesize % step_size)

I don't get it, mtd->writesize < step_size is conceptually
impossible. If that happens, it must be fixed earlier than that.

> +		return -EINVAL;
> +
> +	return mtd->writesize / step_size;
> +}
> +
>  static int sunxi_nfc_maximize_user_data(struct nand_chip *nand, uint32_t oobsize,
>  					int ecc_bytes, int nsectors)
>  {

Thanks,
Miquèl