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

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Date: Wed, 27 Mar 2024 23:15:02 +0100
From: Rafał Miłecki <rafal@...ecki.pl>
To: Christian Marangi <ansuelsmth@...il.com>,
 Miquel Raynal <miquel.raynal@...tlin.com>,
 Richard Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>,
 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 22.03.2024 05:09, Christian Marangi wrote:
> 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;

I think there may be even more unwanted behaviour here. If
mtd_otp_nvmem_register() fails to find node with "user-otp" /
"factory-otp" compatible then it sets "config.of_node" to NULL but that
means NVMEM core still looks for NVMEM cells in device's "of_node".

I believe we should not look for OTP NVMEM cells out of the "user-otp" /
"factory-otp" compatible nodes.

So maybe what we need in the first place is just:
config.add_legacy_fixed_of_cells = !!np;
?

Any extra limitation of .add_legacy_fixed_of_cells should probably be
used only if we want to prevent new users of the legacy syntax. The
problem is that mtd.yaml binding allowed "user-otp" and "factory-otp"
with old syntax cells. It means every MTD device was allowed to have
them.

No in-kernel DTS even used "user-otp" or "factory-otp" with NVMEM legacy
cells but I'm not sure about downstream DTS files. Ideally we would do
config.add_legacy_fixed_of_cells = false;
but that could break compatibility with some downstream DTS files.