Re: [PATCH] spi: spi-qpic-snand: fix calculating of ECC OOB regions' properties

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 7/31/25 8:11 PM, Gabor Juhos wrote:
> The OOB layout used by the driver has two distinct regions which contains
> hardware specific ECC data, yet the qcom_spi_ooblayout_ecc() function sets
> the same offset and length values for both regions which is clearly wrong.
> 
> Change the code to calculate the correct values for both regions.
> 
> For reference, the following table shows the computed offset and length
> values for various OOB size/ECC strength configurations:
> 
>                               +-----------------+-----------------+
>                               |before the change| after the change|
>   +-------+----------+--------+--------+--------+--------+--------+
>   |  OOB  |   ECC    | region | region | region | region | region |
>   |  size | strength | index  | offset | length | offset | length |
>   +-------+----------+--------+--------+--------+--------+--------+
>   |  128  |     8    |    0   |   113  |   15   |    0   |   49   |
>   |       |          |    1   |   113  |   15   |   65   |   63   |
>   +-------+----------+--------+--------+--------+--------+--------+
>   |  128  |     4    |    0   |   117  |   11   |    0   |   37   |
>   |       |          |    1   |   117  |   11   |   53   |   75   |
>   +-------+----------+--------+--------+--------+--------+--------+
>   |   64  |     4    |    0   |    53  |   11   |    0   |   37   |
>   |       |          |    1   |    53  |   11   |   53   |   11   |
>   +-------+----------+--------+--------+--------+--------+--------+
> 
> Fixes: 7304d1909080 ("spi: spi-qpic: add driver for QCOM SPI NAND flash Interface")
> Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
> ---
>  drivers/spi/spi-qpic-snand.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/spi/spi-qpic-snand.c b/drivers/spi/spi-qpic-snand.c
> index 0cfa0d960fd3c245c2bbf4f5e02d0fc0b13e7696..37ddc48d2c17264499f821d235835c4ff5982873 100644
> --- a/drivers/spi/spi-qpic-snand.c
> +++ b/drivers/spi/spi-qpic-snand.c
> @@ -213,8 +213,16 @@ static int qcom_spi_ooblayout_ecc(struct mtd_info *mtd, int section,
>  	if (section > 1)
>  		return -ERANGE;
>  
> -	oobregion->length = qecc->ecc_bytes_hw + qecc->spare_bytes;
> -	oobregion->offset = mtd->oobsize - oobregion->length;
> +	if (!section) {
> +		oobregion->offset = 0;
> +		oobregion->length = qecc->bytes * (qecc->steps - 1) +
> +				    qecc->bbm_size;
> +	} else {
> +		oobregion->offset = qecc->bytes * (qecc->steps - 1) +
> +				    qecc->bbm_size +
> +				    qecc->steps * 4;
> +		oobregion->length = mtd->oobsize - oobregion->offset;
> +	}

How about

if (section == 0) {
} else if (section == 1) {
} else { return -ERANGE }

?

FWIW the values match qcom_spi_ooblayout_free(), so the commit seems
sane

Konrad