linux-kernel - Re: [PATCH v3] mtd: limit OTP NVMEM Cell parse to non Nand devices

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Message-Id: <20240325101834.262354-1-miquel.raynal@bootlin.com>
Date: Mon, 25 Mar 2024 11:18:34 +0100
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Christian Marangi <ansuelsmth@...il.com>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	Rafał Miłecki <rafal@...ecki.pl>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: Re: [PATCH v3] mtd: limit OTP NVMEM Cell parse to non Nand devices

On Fri, 2024-03-22 at 04:09:49 UTC, Christian Marangi wrote:
> 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 detect the MTD type is Nand.
> 
> 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.
> 
> Fixes: 2cc3b37f5b6d ("nvmem: add explicit config option to read old syntax fixed OF cells")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel