[PATCH v3] mtd: limit OTP NVMEM Cell parse to non Nand devices

[Miquel Raynal]

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 at vger.kernel.org>
> Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>

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

Miquel