linux-kernel - Re: [PATCH 2/5] dt-bindings: nvmem: Convert xlnx,zynqmp-nvmem.txt to yaml

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Message-ID: <b5a2d37b-168c-4cc9-9dc0-68f131cdf3ad@linaro.org>
Date:   Fri, 13 Oct 2023 13:58:23 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michal Simek <michal.simek@....com>,
        Praveen Teja Kundanala <praveen.teja.kundanala@....com>,
        srinivas.kandagatla@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] dt-bindings: nvmem: Convert xlnx,zynqmp-nvmem.txt to
 yaml

On 13/10/2023 13:51, Michal Simek wrote:
> 
> 
> On 10/13/23 13:46, Krzysztof Kozlowski wrote:
>> On 13/10/2023 13:22, Michal Simek wrote:
>>>>
>>>>> +
>>>>> +required:
>>>>> +  - compatible
>>>>
>>>> required: block goes after patternProperties: block
>>>>
>>>>> +
>>>>> +patternProperties:
>>>>> +  "^soc_revision@0$":
>>>>
>>>> Why do you define individual memory cells? Is this part of a binding?
>>>> IOW, OS/Linux requires this?
>>>
>>> nvmem has in kernel interface where you can reference to nodes. nvmem_cell_get()
>>> calls. It means you should be able to describe internal layout that's why names
>>> are used. And address in name is there because of reg property is used to
>>> describe base offset and size.
>>
>> That's not really what I am asking. Why internal layout of memory must
>> be part of the bindings?
> 
> It doesn't need to be but offsets are hardcoded inside the driver itself and 
> they can't be different.

Hm, where? I opened drivers/nvmem/zynqmp_nvmem.c and I do not see any
hard-coded offsets.

>  On different nvmem locations like MAC location in 
> eeprom this can vary across boards but in this case location has to be only like 
> this.
> I am fine if they don't need to be actually check but there is no any other way 
> how they can be composed. And also others are not valid that's why not to 
> describe only valid one.

OK, that would be valid (if I find anywhere the offsets) and answers my
questions but I wish it was documented somewhere. Because now you are
making it a binding, so it cannot change (e.g. for different devices
with same hardware but different firmware or manufacturing process, for
future hardware sharing this binding).

In any case the binding should have only items which are really fixed
and OS depends on them. Neither this nor next commit answers this.

Best regards,
Krzysztof