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Date: Thu, 21 Mar 2024 11:32:56 +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>, Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
 =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>, Martin Blumenstingl
 <martin.blumenstingl@googlemail.com>, Claudiu Beznea
 <claudiu.beznea@tuxon.dev>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@collabora.com>, linux-mtd@lists.infradead.org,
 linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] mtd: limit OTP NVMEM Cell parse to non Nand devices
Message-ID: <20240321113256.7e66ac0f@xps-13>
In-Reply-To: <20240321095522.12755-1-ansuelsmth@gmail.com>
References: <20240321095522.12755-1-ansuelsmth@gmail.com>
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Hi Christian,

ansuelsmth@gmail.com wrote on Thu, 21 Mar 2024 10:55:13 +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
> 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.

You forgot to update the commit log :-)

Thanks,
Miqu=C3=A8l