Re: dht11 vs iio-hwmon

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On 27.05.2022 12:31, Dag B wrote:
>
> On 25.05.2022 18:18, Dag B wrote:
>>
>> Hi.
>>
>> I have managed to make use of the dht11 driver and can get data from 
>> my sensor quite reliably.
>>
>> I wanted to be able to read this sensor via lm-sensors, and was 
>> hoping to employ the iio-hwmon bridge for this purpose. Sadly, I do 
>> not get any nodes in the /sys/class/hwmon/ directory for the dht11 
>> sensor.
>>
>> Do iio-drivers (like dht11) have to be written with this bridge in 
>> mind, in order to get the hwmon entries? Or am I just missing a touch 
>> of magic somewhere?
>>
>> root@rpi2:/boot# lsmod | egrep 'iio|hw|dht'
>> dht11                  16384  0
>> iio_hwmon              16384  0
>> raspberrypi_hwmon      16384  0
>> industrialio           81920  2 iio_hwmon,dht11
>> root@rpi2:/boot# cat /sys/bus/iio/devices/iio\:device0/in_temp_input
>> 19400
>> root@rpi2:/boot# ls -l /sys/class/hwmon/
>> total 0
>> lrwxrwxrwx 1 root root 0 May 25 08:59 hwmon0 -> 
>> ../../devices/virtual/thermal/thermal_zone0/hwmon0
>> lrwxrwxrwx 1 root root 0 May 25 08:59 hwmon1 -> 
>> ../../devices/platform/soc/soc:firmware/raspberrypi-hwmon/hwmon/hwmon1
>
>
> So, I have employed my "monkey see, monkey do"-mode. I realize that 
> other iio-drivers got something like this in the device tree 
> specification:
>
>         iio-hwmon {
>
>                 compatible = "iio-hwmon";
>                 io-channels = <&something N>, <&something N+1>;
>
>                 };
>
> Where 'something' most often is 'adc' and N is an integer. 'something' 
> may also be 'tlaNNNN' or 'gpadc'.
>
> 'something' is either defined in the .dts file or an included .dtsi 
> file. I have not yet managed to deduce to what extent these 
> definitions are tied to the device-driver. If someone would be so kind 
> to offer distilled insights, I would really appreciated it. My C-foo 
> is weak, but the itch is real.
>
>
> The dht11 driver provides for temperature and humidity through a 
> single GPIO pin.
>
> drivers/iio/humidity/dht11.c
>
> The .dts file is at:
>
> ./arch/arm/boot/dts/overlays/dht11-overlay.dts
>

The overlay referenced above is obviously not present in the upstream 
kernel. I was working on the Raspberry Pi kernel repo. Managed to 
butcher it to do what I want.

Patch attached for whoever finds themselves in the same position. Also 
posted to relevant RPi forum here:

https://forums.raspberrypi.com/viewtopic.php?t=335329


Dag N


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