linux-kernel - Re: [PATCH 2/4] dt-bindings: hwmon: Added new properties to the devicetree

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Date:   Thu, 14 Sep 2023 07:41:39 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Guenter Roeck <linux@...ck-us.net>,
        Daniel Matyas <daniel.matyas@...log.com>
Cc:     Jean Delvare <jdelvare@...e.com>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-hwmon@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/4] dt-bindings: hwmon: Added new properties to the
 devicetree

On 13/09/2023 18:43, Guenter Roeck wrote:
> On 9/13/23 08:40, Krzysztof Kozlowski wrote:
>> On 13/09/2023 17:21, Daniel Matyas wrote:
>>
>> Subject: not much improved. I am sorry, but you are not adding new
>> properties to entire devicetree of entire world. You are actually not
>> adding anything to any devicetree, because these are bindings (which is
>> obvious, as said by prefix).
>>
>> You got comments on this.
>>
>>> These attributes are:
>>> 	- adi,comp-int - boolean property
>>> 	- adi,alrm-pol - can be 0, 1 (if not present, default value)
>>> 	- adi,flt-q - can be 1, 2, 4, 8 (if not present, default value)
>>> 	- adi,timeout-enable - boolean property
>>
>> Don't repeat what the code does. Explain why you are adding it, what is
>> the purpose.
>>
>>>
>>> These modify the corresponding bits in the configuration register.
>>>
>>> Signed-off-by: Daniel Matyas <daniel.matyas@...log.com>
>>> ---
>>>   .../bindings/hwmon/adi,max31827.yaml          | 35 +++++++++++++++++++
>>>   1 file changed, 35 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml b/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
>>> index 2dc8b07b4d3b..6bde71bdb8dd 100644
>>> --- a/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
>>> +++ b/Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
>>> @@ -32,6 +32,37 @@ properties:
>>>         Must have values in the interval (1.6V; 3.6V) in order for the device to
>>>         function correctly.
>>>   
>>> +  adi,comp-int:
>>> +    description:
>>> +      If present interrupt mode is used. If not present comparator mode is used
>>> +      (default).
>>
>> Why this is a property of hardware?
>>
> 
> Because it affects the behavior of the interrupt signal and whatever
> it is connected to. For example, it could be connected to an interrupt
> controller (interupt mode), or it could be connected to a fan which is
> enabled while the signal is active (comparator mode).

That makes sense. Pardon my naive questions, I just could not figure out
use case out of the field description. Based on this very short
description itself, I could imagine sysfs entry.

> 
>>> +    type: boolean
>>> +
>>> +  adi,alrm-pol:
>>> +    description:
>>> +      Sets the alarms active state.
>>> +            - 0 = active low
>>> +            - 1 = active high
>>> +      For max31827 and max31828 the default alarm polarity is low. For max31829
>>> +      it is high.
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    enum: [0, 1]
>>> +
>>> +  adi,flt-q:
>>> +    description:
>>> +      Select how many consecutive temperature faults must occur before
>>> +      overtemperature or undertemperature faults are indicated in the
>>> +      corresponding status bits.
>>> +      For max31827 default fault queue is 1. For max31828 and max31829 it is 4.
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    enum: [1, 2, 4, 8]
>>> +
>>> +  adi,timeout-enable:
>>> +    description:
>>> +      Enables timeout. Bus timeout resets the I2C-compatible interface when SCL
>>> +      is low for more than 30ms (nominal).
>>
>> Why this is a property of hardware?
>>
> 
> Because it affects i2c bus operation.
> 
> I am not sure I understand what you are trying to say here.
> This is a much a "hardware" property as the i2c bus speed
> and many similar properties, and the need for it is system
> dependent (for example, a system with many devices on the
> i2c bus or with a less than perfect i2c controller may need
> it because the bus tends to get stuck).
> 
> Those are not properties where one would, at runtime,
> decide to enable bus timeout or the interrupt mode or
> the bus speed. Typically that kind of functionality
> has to be configured early when the system is started.
> If devicetree must not or no longer be used to describe the
> system to a point where it can be configured to get it
> to a working state, what is the suggested alternative ?

I could imagine enabling it always, unconditionally. I wanted to
understand why different boards with this chip will have it enabled or
disabled.

Best regards,
Krzysztof