linux-kernel - Re: [PATCH v2] mtd: limit OTP NVMEM Cell parse to non Nand devices

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Date: Thu, 21 Mar 2024 11:32:56 +0100
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Richard Weinberger <richard@....at>, Vignesh Raghavendra
 <vigneshr@...com>, Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
 Rafał Miłecki <rafal@...ecki.pl>, Martin Blumenstingl
 <martin.blumenstingl@...glemail.com>, Claudiu Beznea
 <claudiu.beznea@...on.dev>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@...labora.com>, linux-mtd@...ts.infradead.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] mtd: limit OTP NVMEM Cell parse to non Nand devices

Hi Christian,

ansuelsmth@...il.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.
> 
> 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 consequences.
> 
> 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.
> 
> 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.
> 
> 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.
> 
> 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".
> 
> 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,
Miquèl