linux-kernel - Re: [PATCH v3 1/3] dt-bindings: thermal: sophgo,cv1800-thermal: Add Sophgo CV1800 thermal

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Message-ID: <b5a056f1-a733-4d8b-94ad-49489ff26da2@kernel.org>
Date: Thu, 4 Jul 2024 10:41:39 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Haylen Chu <heylenay@...look.com>, Conor Dooley <conor@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Lukasz Luba <lukasz.luba@....com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Chen Wang <unicorn_wang@...look.com>,
 Inochi Amaoto <inochiama@...look.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Jisheng Zhang <jszhang@...nel.org>, linux-pm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3 1/3] dt-bindings: thermal: sophgo,cv1800-thermal: Add
 Sophgo CV1800 thermal

On 04/07/2024 10:25, Haylen Chu wrote:
> On Tue, Jul 02, 2024 at 05:09:35PM +0200, Krzysztof Kozlowski wrote:
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    enum:
>>>> +      - sophgo,cv1800-thermal
>>>> +
>>>> +  reg:
>>>> +    maxItems: 1
>>>> +
>>>> +  clocks:
>>>> +    description: The thermal sensor clock
>>>> +
>>>> +  interrupts:
>>>> +    maxItems: 1
>>>> +
>>>> +  accumulation-period:
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>> +    description: Accumulation period for a sample
>>>> +    enum:
>>>> +      - 512
>>>> +      - 1024
>>>> +      - 2048
>>>> +      - 4096
>>>> +    default: 2048
>>>> +
>>>> +  chop-period:
>>
>> period in what sort of units? Sounds like time to me, so this would
>> require proper unit suffix.
> 
> In clock ticks.

Then please mention it in the property description.

> 
> When setting to 1024, a time of sample takes (1024 + 2 + 64) clock
> ticks. The clock runs at (25MHz / divider) and the divider is
> configurable.

> 
>>>
>>>> +    description: Period between samples. Should be greater than 524us.
>>>
>>> The constraint here should be "minimum: 524". What's the upper limit?
>>>
>>>> +    default: 1000000
>>>
>>> Rob/Krzysztof, could you comment on the suitability of the three custom
>>> properties here? I know if this was an IIO device, these kinds of things
>>> would be controllable from userspace, and not in the binding. I
>>> mentioned this on the previous version, but I'm not really sure if
>>> thermal devices are somehow different:
>>> https://lore.kernel.org/all/SEYPR01MB4221A739D0645EF0255336EBD7CE2@SEYPR01MB4221.apcprd01.prod.exchangelabs.com/
>>>
>>
>> Why would different boards have different values here? Does it affect
>> accuracy? If so, how much?
>>
>> I doubt there are any boards with different values, thus it sounds like
>> unnecessary tuning parameter.
> 
> Theses values affect accuracy in a minor way (about 1 Celsius degree in
> my test) and could be shared between CV18xx/SG20xx SoCs as they have the
> same design.
> 
> In the first revision, fixed values are used, and I was asked to add
> support for all possible configuration[1]. Now I think this introduces
> extra unnecessary complexity and should be avoided, since this is a
> simple thermal sensor, tuning seems to be useless.
> 
> I suggest renaming "sample-cycle-us" to "sample-rate-hz" and dropping
> other parameters for simplicity.

Ack for me.

Best regards,
Krzysztof