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

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Message-ID: <875xf1hjb8.fsf@bootlin.com>
Date: Tue, 05 Aug 2025 17:36:27 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Mikhail Kshevetskiy <mikhail.kshevetskiy@...sys.eu>
Cc: Richard Weinberger <richard@....at>,  Vignesh Raghavendra
 <vigneshr@...com>,  Lorenzo Bianconi <lorenzo@...nel.org>,  Ray Liu
 <ray.liu@...oha.com>,  Mark Brown <broonie@...nel.org>,  Tudor Ambarus
 <tudor.ambarus@...aro.org>,  Martin Kurbanov
 <mmkurbanov@...utedevices.com>,  Takahiro Kuwano
 <Takahiro.Kuwano@...ineon.com>,  Cheng Ming Lin
 <chengminglin@...c.com.tw>,  linux-mtd@...ts.infradead.org,
  linux-kernel@...r.kernel.org,  linux-arm-kernel@...ts.infradead.org,
  linux-spi@...r.kernel.org
Subject: Re: [PATCH 3/4] drivers: mtd: spi-nand: repeat reading in regular
 mode if continuous reading fails

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