Re: [PATCH v1 09/14] dt-bindings: nvmem: add YAML schema for the sl28 vpd layout

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 31/08/2022 11:17, Michael Walle wrote:
> Am 2022-08-31 09:45, schrieb Krzysztof Kozlowski:
>> On 26/08/2022 00:44, Michael Walle wrote:
>>> Add a schema for the NVMEM layout on Kontron's sl28 boards.
>>>
>>> Signed-off-by: Michael Walle <michael@walle.cc>
>>> ---
>>>  .../nvmem/layouts/kontron,sl28-vpd.yaml       | 52 
>>> +++++++++++++++++++
>>>  1 file changed, 52 insertions(+)
>>>  create mode 100644 
>>> Documentation/devicetree/bindings/nvmem/layouts/kontron,sl28-vpd.yaml
>>>
>>> diff --git 
>>> a/Documentation/devicetree/bindings/nvmem/layouts/kontron,sl28-vpd.yaml 
>>> b/Documentation/devicetree/bindings/nvmem/layouts/kontron,sl28-vpd.yaml
>>> new file mode 100644
>>> index 000000000000..e4bc2d9182db
>>> --- /dev/null
>>> +++ 
>>> b/Documentation/devicetree/bindings/nvmem/layouts/kontron,sl28-vpd.yaml
>>> @@ -0,0 +1,52 @@
>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: 
>>> http://devicetree.org/schemas/nvmem/layouts/kontron,sl28-vpd.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: NVMEM layout of the Kontron SMARC-sAL28 vital product data
>>> +
>>> +maintainers:
>>> +  - Michael Walle <michael@walle.cc>
>>> +
>>> +description:
>>> +  The vital product data (VPD) of the sl28 boards contains a serial
>>> +  number and a base MAC address. The actual MAC addresses for the
>>> +  on-board ethernet devices are derived from this base MAC address by
>>> +  adding an offset.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    items:
>>> +      - const: kontron,sl28-vpd
>>> +      - const: user-otp
>>> +
>>> +  serial-number:
>>> +    type: object
>>
>> You should define the contents of this object. I would expect this to 
>> be
>> uint32 or string. I think you also need description, as this is not
>> really standard field.
> 
> First thing, this binding isn't like the usual ones, so it might be
> totally wrong.
> 
> What I'd like to achieve here is the following:
> 
> We have the nvmem-consumer dt binding where you can reference a
> nvmem cell in a consumer node. Example:
>    nvmem-cells = <&base_mac_address 5>;
>    nvmem-cell-names = "mac-address";
> 
> On the other end of the link we have the nvmem-provider. The dt
> bindings works well if that one has individual cell nodes, like
> it is described in the nvmem.yaml binding. I.e. you can give the
> cell a label and make a reference to it in the consumer just like
> in the example above.

You can also achieve it with phandle argument to the nvmwm controller,
right? Just like most of providers are doing (clocks, resets). Having
fake (empty) nodes just for that seems like overkill.

> 
> Now comes the catch: what if there is no actual description of the
> cell in the device tree, but is is generated during runtime. How
> can I get a label to it.

Same as clocks, resets, power-domains and everyone else.


> Therefore, in this case, there is just
> an empty node and the driver will associate it with the cell
> created during runtime (see patch 10). It is not expected, that
> is has any properties.

It cannot be even referenced as it does not have #cells property...

> 
>>> +
>>> +  base-mac-address:
>>
>> Fields should be rather described here, not in top-level description.
>>
>>> +    type: object
>>
>> On this level:
>>     additionalProperties: false
>>
>>> +
>>> +    properties:
>>> +      "#nvmem-cell-cells":
>>> +        const: 1
>>> +
>>
>> I also wonder why you do not have unit addresses. What if you want to
>> have two base MAC addresses?
> 
> That would describe an offset within the nvmem device. But the offset
> might not be constant, depending on the content. My understanding
> so far was that in that case, you use the "-N" suffix.
> 
> base-mac-address-1
> base-mac-address-2
> 
> (or maybe completely different names).

You do not allow "base-mac-address-1". Your binding explicitly accepts
only "base-mac-address".

Best regards,
Krzysztof