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

[Christian Marangi]

On Wed, Mar 27, 2024 at 11:15:02PM +0100, Rafał Miłecki wrote:
> 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.

Yes the main problem is prevent regression in downstream. I feel for the
nand usage, this is 100% of the times broken. For SPI and other corner
case MTD devices it's not?

Anyway did you by chance have a suggestion for a better fixes tag?

-- 
	Ansuel