Received-SPF: pass (google.com: domain of linux-kernel+bounces-149617-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Thu, 18 Apr 2024 08:48:08 +0200
From: Sascha Hauer <s.hauer@pengutronix.de>
To: Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>
Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/4] mtd: nand: mxc_nand: disable subpage reads
Message-ID: <ZiDCKGlG4MZ23Tqo@pengutronix.de>
References: <20240417-mtd-nand-mxc-nand-exec-op-v1-0-d12564fe54e9@pengutronix.de>
 <20240417-mtd-nand-mxc-nand-exec-op-v1-4-d12564fe54e9@pengutronix.de>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240417-mtd-nand-mxc-nand-exec-op-v1-4-d12564fe54e9@pengutronix.de>

On Wed, Apr 17, 2024 at 09:13:31AM +0200, Sascha Hauer wrote:
> The NAND core enabled subpage reads when a largepage NAND is used with
> SOFT_ECC. The i.MX NAND controller doesn't support subpage reads, so
> clear the flag again.
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>  drivers/mtd/nand/raw/mxc_nand.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/mxc_nand.c b/drivers/mtd/nand/raw/mxc_nand.c
> index f44c130dca18d..19b46210bd194 100644
> --- a/drivers/mtd/nand/raw/mxc_nand.c
> +++ b/drivers/mtd/nand/raw/mxc_nand.c
> @@ -1667,6 +1667,8 @@ static int mxcnd_probe(struct platform_device *pdev)
>  	if (err)
>  		goto escan;
>  
> +	this->options &= ~NAND_SUBPAGE_READ;
> +

Nah, it doesn't work like this. It turns out the BBT is read using
subpage reads before we can disable them here.

This is the code in nand_scan_tail() we stumble upon:

	/* Large page NAND with SOFT_ECC should support subpage reads */
	switch (ecc->engine_type) {
	case NAND_ECC_ENGINE_TYPE_SOFT:
		if (chip->page_shift > 9)
			chip->options |= NAND_SUBPAGE_READ;
		break;

	default:
		break;
	}

So the code assumes subpage reads are ok when SOFT_ECC is in use, which
in my case is not true. I guess some drivers depend on the
NAND_SUBPAGE_READ bit magically be set, so simply removing this code is
likely not an option.  Any ideas what to do?

Sascha


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |