[PATCH v4] mtd: limit OTP NVMEM Cell parse to non Nand devices

[Miquel Raynal]

Hi Christian,

ansuelsmth at gmail.com wrote on Tue,  2 Apr 2024 23:23:19 +0200:

> MTD OTP logic is very fragile on parsing NVMEM Cell and can be
> problematic with some specific kind of devices.
> 
> The problem was discovered by e87161321a40 ("mtd: rawnand: macronix:
> OTP access for MX30LFxG18AC") where OTP support was added to a NAND
> device. With the case of NAND devices, it does require a node where ECC
> info are declared and all the fixed partitions, and this cause the OTP
> codepath to parse this node as OTP NVMEM Cells, making probe fail and
> the NAND device registration fail.
> 
> MTD OTP parsing should have been limited to always using compatible to
> prevent this error by using node with compatible "otp-user" or
> "otp-factory".
> 
> NVMEM across the years had various iteration on how Cells could be
> declared in DT, in some old implementation, no_of_node should have been
> enabled but now add_legacy_fixed_of_cells should be used to disable
> NVMEM to parse child node as NVMEM Cell.
> 
> 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: 4b361cfa8624 ("mtd: core: add OTP nvmem provider support")
> Cc: <stable at vger.kernel.org> # v6.7+
> Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>

Feels okay to me, but I'd like to get validation from Rafał as well who
extensively worked on this aspect and must have a sharpened eyed for
this kind of issue :-)

> ---
> 
> To backport this to v6.6 and previous,
> 
> config.no_of_node = mtd_type_is_nand(mtd);
> 
> should be used as it does pose the same usage of
> add_legacy_fixed_of_cells.
> 
> Changes v4:
> - Add info on how to backport this to previous kernel
> - Fix Fixes tag
> - Reformat commit description as it was unprecise and
>   had false statement
> Changes v3:
> - Fix commit description
> Changes v2:
> - Use mtd_type_is_nand instead of node name check
> 
>  drivers/mtd/mtdcore.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 5887feb347a4..0de87bc63840 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -900,7 +900,7 @@ static struct nvmem_device
> *mtd_otp_nvmem_register(struct mtd_info *mtd, config.name =
> compatible; config.id = NVMEM_DEVID_AUTO;
>  	config.owner = THIS_MODULE;
> -	config.add_legacy_fixed_of_cells = true;
> +	config.add_legacy_fixed_of_cells = !mtd_type_is_nand(mtd);
>  	config.type = NVMEM_TYPE_OTP;
>  	config.root_only = true;
>  	config.ignore_wp = true;


Thanks,
Miquèl