Re: [PATCH 0/5] mtd: core: OTP nvmem provider support

[Michael Walle]

Hi Rob,

Am 2021-04-16 20:44, schrieb Rob Herring:
> On Fri, Apr 16, 2021 at 01:49:23PM +0200, Michael Walle wrote:
> > The goal is to fetch a (base) MAC address from the OTP region of a SPI 
> > NOR
> > flash.
> >
> > This is the first part, where I try to add the nvmem provider support 
> > to
> > the MTD core.
> >
> > I'm not sure about the device tree bindings. Consider the following 
> > two
> > variants:
> >
> > (1)
> >     flash@0 {
> >         ..
> >
> >         otp {
> >             compatible = "mtd-user-otp";
>
> mtd is a linuxism. Why not just 'nvmem-cells' here or as a fallback if
> we come up with a better name?

There are two different compatibles: "mtd-user-otp" and 
"mtd-factory-otp"
to differentiate what kind of OTP should be used (and both are possible
at the same time). Thus nvmem-cells alone won't be enough. We could drop
the "mtd-" prefix though.

Is there a benefit of having the following?
  compatible = "user-otp", "nvmem-cells";


> >             #address-cells = <1>;
> >             #size-cells = <1>;
> >
> >             serial-number@0 {
> >                 reg = <0x0 0x8>;
> >             };
> >         };
> >     };
> >
> > (2)
> >     flash@0 {
> >         ..
> >
> >         otp {
> >             compatible = "mtd-user-otp";
> >             #address-cells = <1>;
> >             #size-cells = <1>;
> >
> > 			some-useful-name {
> >                 compatible = "nvmem-cells";
> >
> >                 serial-number@0 {
> >                     reg = <0x0 0x8>;
> >                 };
> > 			};
> >         };
> >     };
> >
> > Both bindings use a subnode "opt[-N]". We cannot have the nvmem cells 
> > as
> > children to the flash node because of the legacy partition binding.
> >
> > (1) seems to be the form which is used almost everywhere in the 
> > kernel.
> > That is, the nvmem cells are just children of the parent node.
> >
> > (2) seem to be more natural, because there might also be other 
> > properties
> > inside the otp subnode and might be more future-proof.
> >
> > At the moment this patch implements (1).
>
> I think approach (1) seems fine.

ok

-michael