Re: [PATCH v2] mtd: rawnand: sunxi: fit maximized ECC step to page size

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] ECC strength maximization overestimates available capacity for 512-byte pages due to a bit-length calculation mismatch, causing initialization failures.
--

commit de85ead656c2f999d69dec7e2c0a592634ba071e
Author: James Hilliard <james.hilliard1@gmail.com>

mtd: rawnand: sunxi: fit maximized ECC step to page size

This commit addresses an issue where maximizing ECC strength for a NAND
with a 512-byte page yields zero ECC steps. It modifies the driver to
dynamically select a 512-byte step for 512-byte pages, while retaining
1024-byte steps for larger pages.

> diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
> index 83666dd6cb2a8..de1e6b49f79aa 100644
> --- a/drivers/mtd/nand/raw/sunxi_nand.c
> +++ b/drivers/mtd/nand/raw/sunxi_nand.c
> @@ -2084,7 +2084,7 @@ 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;
>  
> -		ecc->size = 1024;
> +		ecc->size = min_t(unsigned int, mtd->writesize, 1024);

[Severity: High]
Does setting ecc->size to 512 for 512-byte pages cause a bit-length
calculation mismatch downstream?

When ecc->size is 512, the maximum ECC strength is estimated using 13 bits
per symbol (fls(4096)):

sunxi_nand_hw_ecc_ctrl_init() {
    ...
		ecc->strength = bytes * 8 / fls(8 * ecc->size);
    ...
}

However, the driver later unconditionally calculates the required ECC bytes
assuming 14 bits per symbol:

sunxi_nand_hw_ecc_ctrl_init() {
    ...
	/* HW ECC always request ECC bytes for 1024 bytes blocks */
	ecc->bytes = DIV_ROUND_UP(ecc->strength * fls(8 * 1024), 8);
    ...
}

This mismatch overestimates the maximum strength. For example, with 26
available OOB bytes, the 13-bit estimation incorrectly selects a strength of
16, but the 14-bit calculation requires 28 bytes. 

The subsequent bounds check:

sunxi_nand_hw_ecc_ctrl_init() {
    ...
	if (mtd->oobsize < (ecc->bytes * nsectors + total_user_data_sz))
		return -EINVAL;
    ...
}

then fails, causing the driver probe to abort for 512-byte page devices when
nand-ecc-maximize is enabled.

>  		nsectors = mtd->writesize / ecc->size;
>  
>  		if (!nfc->caps->reg_user_data_len) {

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260904-submit-sunxi-nand-ecc-step-validation-v2-1-6e3ba6200948@gmail.com?part=1