Re: [PATCH 3/8] dt-bindings: hwmon: Allow specifying channels for lm90

From: Guenter Roeck <linux@roeck-us.net>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	Slawomir Stepien <sst@poczta.fm>,
	linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org
Cc: jdelvare@suse.com, robh+dt@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, przemyslaw.cencner@nokia.com,
	krzysztof.adamski@nokia.com, alexander.sverdlin@nokia.com,
	Slawomir Stepien <slawomir.stepien@nokia.com>
Subject: Re: [PATCH 3/8] dt-bindings: hwmon: Allow specifying channels for lm90
Date: Fri, 20 May 2022 07:22:42 -0700	[thread overview]
Message-ID: <f124cbcb-3fca-3f1c-f47e-730f15c1f074@roeck-us.net> (raw)
In-Reply-To: <b5ff0f2c-d741-6dec-c306-b54cb5075ccf@linaro.org>

On 5/20/22 07:09, Krzysztof Kozlowski wrote:
> On 20/05/2022 15:42, Guenter Roeck wrote:
>>>
>>>> +          A descriptive name for this channel, like "ambient" or "psu".
>>>> +
>>>> +      offset:
>>>> +        description: |
>>>
>>> This does not look like standard property, so you need vendor and unit
>>> suffix.
>>>
>>
>> Temperature offset is a standard property for temperature sensor
> 
> The original description was strictly connected to registers, so that
> one as not a standard. It seems it was just a wording...
> 
>> chips with external channels, implemented by a diode or transistor.
>> Making it non-standard will mean that we'll have lots of
>> "vendor,offset" properties, one each for each vendor selling
>> temperature sensor chips with external channels. This gets
>> more complicated here because the lm90 driver does support chips
>> from several different vendors. Almost all of them support
>> this functionality. Which vendor do you select in this case ?
>>
>> I would suggest to use temperature-offset-milliseconds, though.
> 
> Yes, this sounds good. Just not seconds but millicelsius, I guess?
> 

Uuh, yes. Sorry, must be too early in the morning here.

>>
>>>> +          The value (millidegree Celsius) to be programmed in the channel specific offset register
>>>> +          (if supported by device).
>>>
>>> You described programming model which should not be put in the bindings.
>>> Please describe the hardware.
>>>
>>
>> It is a configuration value, which is hardware dependent because
>> it depends on the temperature diode or transistor connected to the chip.
> 
> Sure, so this could be reworded "Offset against some base value for each
> channel temperature", or something similar (you know better than me).
> Referring to registers and where exactly this should be programmed in
> the device is related to device programming model, not to bindings.
> 

Maybe something like "Temperature offset to be added to or
subtracted from remote temperature measurements".

Thanks,
Guenter