Re: [PATCH 3/4] drivers: mtd: spi-nand: repeat reading in regular mode if continuous reading fails

[Miquel Raynal <miquel.raynal@bootlin.com>]

On 04/08/2025 at 22:21:31 +03, Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu> wrote:

> Continuous reading may result in multiple flash pages reading in one
> operation. Unfortunately, not all spi-nand controllers support such
> large reading. They will read less data. Unfortunately, the operation
> can't be continued.
>
> In this case:
>  * disable continuous reading on this (not good enough) spi controller
>  * repeat reading in regular mode.
>
> Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>
> ---
>  drivers/mtd/nand/spi/core.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
> index ff6a1e2fcfdc..88e4c00cccc4 100644
> --- a/drivers/mtd/nand/spi/core.c
> +++ b/drivers/mtd/nand/spi/core.c
> @@ -431,7 +431,7 @@ static int spinand_read_from_cache_op(struct spinand_device *spinand,
>  		 * Toggling the CS during a continuous read is forbidden.
>  		 */
>  		if (nbytes && req->continuous)
> -			return -EIO;
> +			return -E2BIG;
>  	}
>  
>  	if (req->datalen)
> @@ -893,15 +893,26 @@ static int spinand_mtd_read(struct mtd_info *mtd, loff_t from,
>  	struct spinand_device *spinand = mtd_to_spinand(mtd);
>  	struct mtd_ecc_stats old_stats;
>  	unsigned int max_bitflips = 0;
> -	int ret;
> +	int ret = -E2BIG;
>  
>  	mutex_lock(&spinand->lock);
>  
>  	old_stats = mtd->ecc_stats;
>  
> -	if (spinand_use_cont_read(mtd, from, ops))
> +	if (spinand_use_cont_read(mtd, from, ops)) {
>  		ret = spinand_mtd_continuous_page_read(mtd, from, ops, &max_bitflips);
> -	else
> +		if (ret == -E2BIG) {
> +			/*
> +			 * Some spi controllers may not support reading up to
> +			 * erase block size. They will read less data than
> +			 * expected. If this happen disable continuous mode

                                             happens,

> +			 * and repeat reading in normal mode.
> +			 */
> +			spinand->cont_read_possible = false;
> +		}
> +	}
> +
> +	if (ret == -E2BIG)

While I agree with the overall logic, I find pretty unreadable to
perform the regular read upon a return value that is an error code set
in the init sequence. Can you please propose an alternate implementation?

>  		ret = spinand_mtd_regular_page_read(mtd, from, ops, &max_bitflips);
>  
>  	if (ops->stats) {

Thanks!
Miquèl