linux-kernel - Re: [PATCH v2 1/2] iio: adc: hx711: Add DT binding for avia,hx711

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Message-ID: <10cef06e-a3d0-ef9e-2a6a-b044f02d8df3@metafoo.de>
Date:   Wed, 14 Dec 2016 12:18:11 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Andreas Klinger <ak@...klinger.de>
Cc:     devicetree@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        pawel.moll@....com, mark.rutland@....com,
        ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
        jic23@...nel.org, knaack.h@....de, pmeerw@...erw.net
Subject: Re: [PATCH v2 1/2] iio: adc: hx711: Add DT binding for avia,hx711

On 12/14/2016 11:34 AM, Andreas Klinger wrote:
> Hi Lars-Peter,
> 
> Lars-Peter Clausen <lars@...afoo.de> schrieb am Wed, 14. Dec 11:11:
>> On 12/14/2016 10:59 AM, Andreas Klinger wrote:
>>> Add DT bindings for avia,hx711
>>> Add vendor avia to vendor list
>>>
>>> Signed-off-by: Andreas Klinger <ak@...klinger.de>
>>> ---
>>>  .../devicetree/bindings/iio/adc/avia-hx711.txt      | 21 +++++++++++++++++++++
>>>  .../devicetree/bindings/vendor-prefixes.txt         |  1 +
>>>  2 files changed, 22 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/iio/adc/avia-hx711.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt b/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt
>>> new file mode 100644
>>> index 000000000000..6a4659fc7a4f
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/iio/adc/avia-hx711.txt
>>> @@ -0,0 +1,21 @@
>>> +* AVIA HX711 ADC chip for weight cells
>>> +  Bit-banging driver
>>> +
>>> +Required properties:
>>> + - compatible: Should be "avia,hx711"
>>> + - sck-gpios:	Definition of the GPIO for the clock
>>> + - dout-gpios:	Definition of the GPIO for data-out
>>> +		See Documentation/devicetree/bindings/gpio/gpio.txt
>>> +
>>> +Recommended properties:
>>> + - gain:	Gain select, can be 32, 64 or 128
>>> +		default is 128
>>
>> If the gain is software programmable it should be exposed by the driver
>> allowing the application to change it rather than putting it in the devicetree.
>>
> There is also a hardware dependency in terms of where to connect the input
> channel to:
> - gain 64 and gain 128 are available only on input channel A
> - gain 32 is only available on input channel B
> 
> Do you still think, it should be removed from the devicetree?

I believe so, especially considering that there are two channels and your
driver currently only exposes one of them, which is elected by the gain
configuration. I'd expect that there are use-cases where both inputs are
connected and the application wants to switch between them dynamically at
runtime.

The only tricky part here seems to be that the configuration for the next
conversion is selected on the current conversion. This means you probably
need to do a dummy conversion whenever the settings change.