When nand-ecc-maximize is set, the driver selects a 1024-byte ECC step
and divides the available OOB bytes by the resulting number of steps. A
NAND with a smaller page therefore produces zero steps and a division by
zero.

The older controllers also provide a 512-byte ECC block mode, but the
hardware documentation describes that as an ECC block size within NAND
pages whose supported sizes start at 1024 bytes. It does not document a
512-byte NAND page mode.

Reject pages smaller than 1024 bytes before deriving the step count. This
prevents the division by zero at the point where the incompatible
maximized geometry is selected without changing explicitly configured
512-byte ECC block handling.

Fixes: 4796d8655915 ("mtd: nand: sunxi: Support ECC maximization")
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
Changes in v3:
- reject ECC maximization on pages smaller than 1024 bytes instead of
  selecting the 512-byte ECC block mode
- leave explicitly configured 512-byte ECC block handling unchanged
- clarify that the hardware documentation describes 512 bytes as an ECC
  block size rather than a supported NAND page size
- Link to v2: https://patch.msgid.link/20260904-submit-sunxi-nand-ecc-step-validation-v2-1-6e3ba6200948@gmail.com

Changes in v2:
- fix ECC maximization at its source by selecting a 512-byte step for
  512-byte pages instead of validating the derived step count
- retain 1024-byte steps for larger pages and the existing capability checks
- rebase on the current MTD nand/next branch
- Link to v1: https://patch.msgid.link/20260811060651.227431-1-james.hilliard1@gmail.com
---
 drivers/mtd/nand/raw/sunxi_nand.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
index 83666dd6cb2a..c84f304fb749 100644
--- a/drivers/mtd/nand/raw/sunxi_nand.c
+++ b/drivers/mtd/nand/raw/sunxi_nand.c
@@ -2084,6 +2084,9 @@ static int sunxi_nand_hw_ecc_ctrl_init(struct nand_chip *nand,
 	if (nanddev->ecc.user_conf.flags & NAND_ECC_MAXIMIZE_STRENGTH) {
 		int bytes = mtd->oobsize;
 
+		if (mtd->writesize < 1024)
+			return -EINVAL;
+
 		ecc->size = 1024;
 		nsectors = mtd->writesize / ecc->size;
 

---
base-commit: def559a215699aa2f2d8ef98f30156b9d562a154
change-id: 20260904-submit-sunxi-nand-ecc-step-validation-0e571088b5e7

Best regards,
--  
James Hilliard <james.hilliard1@gmail.com>

On Fri, 04 Sep 2026 19:05:37 -0600, James Hilliard wrote:
> When nand-ecc-maximize is set, the driver selects a 1024-byte ECC step
> and divides the available OOB bytes by the resulting number of steps. A
> NAND with a smaller page therefore produces zero steps and a division by
> zero.
> 
> The older controllers also provide a 512-byte ECC block mode, but the
> hardware documentation describes that as an ECC block size within NAND
> pages whose supported sizes start at 1024 bytes. It does not document a
> 512-byte NAND page mode.
> 
> [...]

Applied to nand/next, thanks!

[1/1] mtd: rawnand: sunxi: reject ECC maximization on small pages
      commit: a3c84084a73e170374b7dd493947efdef4ee57bc

Patche(s) should be available on mtd/linux.git and will be
part of the next PR (provided that no robot complains by then).

Kind regards,
Miquèl