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

[Michael Walle]

Hi Rob,

Am 2021-04-20 16:08, schrieb Rob Herring:
> On Fri, Apr 16, 2021 at 09:26:03PM +0200, Michael Walle wrote:
> > 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";
>
> Yes. I assume 'user-otp' tells you something about the region and
> 'nvmem-cells' tells you that there are child nodes of nvmem data. Of
> course 'user-otp' could imply 'nvmem-cells' as you did. I'm fine with
> either way.

Ah, if I use both compatibles, then the
Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml
schema kicks in, which mandates 'compatible = "nvmem-cells";' and I
get the following errors:

  CHECK   Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml
/home/mwalle/repos/b-linux-arm64/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: 
otp-1: compatible:0: 'nvmem-cells' was expected
	From schema: 
/home/mwalle/repos/linux-mw/Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml
/home/mwalle/repos/b-linux-arm64/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: 
otp-1: compatible: ['factory-otp', 'nvmem-cells'] is too long
	From schema: 
/home/mwalle/repos/linux-mw/Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml
/home/mwalle/repos/b-linux-arm64/Documentation/devicetree/bindings/mtd/mtd.example.dt.yaml: 
otp-1: compatible: Additional items are not allowed ('nvmem-cells' was 
unexpected)
	From schema: 
/home/mwalle/repos/linux-mw/Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml

Is there a way around that?

-michael