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Date: Thu, 21 Mar 2024 08:17:05 +0100
From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Christian Marangi <ansuelsmth@gmail.com>
Cc: Richard Weinberger <richard@nod.at>, Vignesh Raghavendra
 <vigneshr@ti.com>, Jernej Skrabec <jernej.skrabec@gmail.com>, Greg
 Kroah-Hartman <gregkh@linuxfoundation.org>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@collabora.com>, Martin Blumenstingl
 <martin.blumenstingl@googlemail.com>, =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?=
 <rafal@milecki.pl>, linux-mtd@lists.infradead.org,
 linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] mtd: limit OTP NVMEM Cell parse to non Nand devices
Message-ID: <20240321081705.597f72bf@xps-13>
In-Reply-To: <20240320162927.5015-1-ansuelsmth@gmail.com>
References: <20240320162927.5015-1-ansuelsmth@gmail.com>
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Hi Christian,

ansuelsmth@gmail.com wrote on Wed, 20 Mar 2024 17:29:25 +0100:

> MTD OTP logic is very fragile and can be problematic with some specific
> kind of devices.
>=20
> NVMEM across the years had various iteration on how Cells could be
> declared in DT and MTD OTP probably was left behind and
> add_legacy_fixed_of_cells was enabled without thinking of the consequence=
s.
>=20
> That option enables NVMEM to scan the provided of_node and treat each
> child as a NVMEM Cell, this was to support legacy NVMEM implementation
> and don't cause regression.
>=20
> This is problematic if we have devices like Nand where the OTP is
> triggered by setting a special mode in the flash. In this context real
> partitions declared in the Nand node are registered as OTP Cells and
> this cause probe fail with -EINVAL error.
>=20
> This was never notice due to the fact that till now, no Nand supported
> the OTP feature. With commit e87161321a40 ("mtd: rawnand: macronix: OTP
> access for MX30LFxG18AC") this changed and coincidentally this Nand is
> used on an FritzBox 7530 supported on OpenWrt.
>=20
> Alternative and more robust way to declare OTP Cells are already
> prossible by using the fixed-layout node or by declaring a child node
> with the compatible set to "otp-user" or "otp-factory".
>=20
> To fix this and limit any regression with other MTD that makes use of
> declaring OTP as direct child of the dev node, disable

The beauty of backward compatibility...

> add_legacy_fixed_of_cells if we have a node called nand since it's the
> standard property name to identify Nand devices attached to a Nand
> Controller.
>=20
> With the following logic, the OTP NVMEM entry is correctly created with
> no Cells and the MTD Nand is correctly probed and partitions are
> correctly exposed.

Thanks for the investigation and the fix. An implementation detail
below.

>=20
> Fixes: 2cc3b37f5b6d ("nvmem: add explicit config option to read old synta=
x fixed OF cells")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
> ---
>  drivers/mtd/mtdcore.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 5887feb347a4..6872477a5129 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -900,7 +900,7 @@ static struct nvmem_device *mtd_otp_nvmem_register(st=
ruct mtd_info *mtd,
>  	config.name =3D compatible;
>  	config.id =3D NVMEM_DEVID_AUTO;
>  	config.owner =3D THIS_MODULE;
> -	config.add_legacy_fixed_of_cells =3D true;
> +	config.add_legacy_fixed_of_cells =3D !of_node_name_eq(mtd->dev.of_node,=
 "nand");

Could we use mtd_type_is_nand() instead?

>  	config.type =3D NVMEM_TYPE_OTP;
>  	config.root_only =3D true;
>  	config.ignore_wp =3D true;

Thanks,
Miqu=C3=A8l