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

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Message-ID: <9f33229a8fe83b49210289fc93a8554e@walle.cc>
Date:   Fri, 16 Apr 2021 21:26:03 +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 2021-04-16 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