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

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Message-ID: <755f8f930844cbef2b32f81bf6585c31@walle.cc>
Date:   Tue, 20 Apr 2021 17:03:52 +0200
From:   Michael Walle <michael@...le.cc>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: Re: [PATCH 0/5] mtd: core: OTP nvmem provider support

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