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

Miquel Raynal
2024-03-21T10:33:02Z

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.
>
> 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