linux-kernel - Re: [PATCH 1/2] dt-bindings: hwmon: add binding documentation for adt7475

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Message-ID: <46001dee3a224ac3b01ceb11421af83d@svr-chch-ex1.atlnz.lc>
Date:   Thu, 8 Nov 2018 19:55:39 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Guenter Roeck <linux@...ck-us.net>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "jdelvare@...e.com" <jdelvare@...e.com>
CC:     "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/2] dt-bindings: hwmon: add binding documentation for
 adt7475

On 7/11/18 6:08 PM, Guenter Roeck wrote:
> On 11/6/18 8:27 PM, Chris Packham wrote:
>> On 7/11/18 5:24 PM, Guenter Roeck wrote:
>>> On 11/6/18 8:00 PM, Chris Packham wrote:
>>>> With the addition of the invert-pwm property the adt7475 needs its own
>>>> binding documentation rather being captured under trivial-devices.txt.
>>>>
>>>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>>>> ---
>>>>      .../devicetree/bindings/hwmon/adt7475.txt     | 22 +++++++++++++++++++
>>>>      .../devicetree/bindings/trivial-devices.txt   |  4 ----
>>>>      2 files changed, 22 insertions(+), 4 deletions(-)
>>>>      create mode 100644 Documentation/devicetree/bindings/hwmon/adt7475.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/hwmon/adt7475.txt b/Documentation/devicetree/bindings/hwmon/adt7475.txt
>>>> new file mode 100644
>>>> index 000000000000..79255439e157
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/hwmon/adt7475.txt
>>>> @@ -0,0 +1,22 @@
>>>> +*ADT7475 hwmon sensor.
>>>> +
>>>> +Required properties:
>>>> +- compatible: One of
>>>> +	"adi,adt7473"
>>>> +	"adi,adt7475"
>>>> +	"adi,adt7476"
>>>> +	"adi,adt7490"
>>>> +
>>>> +- reg: I2C address
>>>> +
>>>> +optional properties:
>>>> +
>>>> +- invert-pwm: This configures the PWM to use logic low for 100% duty cycle.
>>>> +
>>>> +Example:
>>>> +
>>>> +hwmon@2e {
>>>> +	compatible = ;
>>>> +	reg = <0x2e>;
>>>> +	invert-pwm;
>>>
>>> If I understand correctly, the flag is set per pwm channel. A single global
>>> property seems inappropriate.
>>
>> Yes it is per-channel. But I was having a hard time imagining a hardware
>> design that would use both inverted and non-inverted at the same time.
>>
> 
> People can be inventive. Sometimes too much so.
> 
>> Do you have a preference for how the properties should look?
>>
>>      invert-pwm[123]?
>>
>>      invert-pwm = <0x7>;?
>>
> Ultimately we'll have to find a generic way of defining devicetree properties for
> hardware monitoring devices, not just for pwm but for all sensor types. A sub-node
> per channel seems to be the most likely answer, but I think that is a long way off
> (and will require lengthy discussions about acceptable properties).
> 
> I was looking into pwm DT properties, but they define a set of flags
> (PWM_POLARITY_INVERTED, PWM_POLARITY_NORMAL).
> 
> The g762 driver uses "pwm_polarity". Underscore - hmm. Other drivers use module
> parameters, sysfs attributes (pwmX_invert in asc7621 driver), or platform data
> (g762, max6639).
> 
> Maybe pwm-polarity = <PWM_POLARITY_NORMAL | PWM_POLARITY_INVERTED> ?
> No idea if that makes sense. Or just a boolean pwm-polarity-inverted.

That would allow undoing an earlier invert which is something my initial 
implementation lacked.

In the future we could also make this a list of values to deal with 
multiple pwm outputs

e.g. pwm-polarity = <PWM_POLARITY_NORMAL>, <PWM_POLARITY_NORMAL> 
<PWM_POLARITY_INVERTED>;

I'll look at a v2 that does the first part for now.

> 
> Thinking about it per channel vs. per chip ... other drivers also seem to
> use a single property / attribute for the entire chip, so that is fine here
> as well. We can always extend it if needed.
> 
> Anyway, I am fine with whatever Rob accepts.
> 
> Guenter
> 
>>>
>>> Guenter
>>>
>>>> +};
>>>> diff --git a/Documentation/devicetree/bindings/trivial-devices.txt b/Documentation/devicetree/bindings/trivial-devices.txt
>>>> index 69c934aec13b..4f29100d6bbf 100644
>>>> --- a/Documentation/devicetree/bindings/trivial-devices.txt
>>>> +++ b/Documentation/devicetree/bindings/trivial-devices.txt
>>>> @@ -14,10 +14,6 @@ ad,ad7414		SMBus/I2C Digital Temperature Sensor in 6-Pin SOT with SMBus Alert an
>>>>      ad,adm9240		ADM9240:  Complete System Hardware Monitor for uProcessor-Based Systems
>>>>      adi,adt7461		+/-1C TDM Extended Temp Range I.C
>>>>      adt7461			+/-1C TDM Extended Temp Range I.C
>>>> -adi,adt7473		+/-1C TDM Extended Temp Range I.C
>>>> -adi,adt7475		+/-1C TDM Extended Temp Range I.C
>>>> -adi,adt7476		+/-1C TDM Extended Temp Range I.C
>>>> -adi,adt7490		+/-1C TDM Extended Temp Range I.C
>>>>      adi,adxl345		Three-Axis Digital Accelerometer
>>>>      adi,adxl346		Three-Axis Digital Accelerometer (backward-compatibility value "adi,adxl345" must be listed too)
>>>>      ams,iaq-core		AMS iAQ-Core VOC Sensor
>>>>
>>>
>>>
>>
>>
> 
>