I have a DHT22 temperature and humidity sensor that I’d like to use with my BeagleBone Black. A kind soul has written a GPIO driver for the device, and when I contacted him, he even tried to help me get it running on my BBB. Problem is, he has another device, and like me, isn’t familiar with the BBB’s device tree configuration. The driver in question is available in two patches:
http://marc.info/?l=linux-iio&m=138270184408677&w=2
http://marc.info/?l=linux-iio&m=138270172108628&w=2
The patches apply cleanly and build without issue using Robert Nelson’s 3.12.1-bone8 (these scripts are fantastic, thanks!).
I have the sensor’s data wire connected to P9 27. In my attempts to make this work, I modified arch/arm/boot/dts/am335x-bone-common.dtsi as follows:
At the bottom of the first section (the one that starts with “/ {”, I suppose this is the root?), I added:
humidity_sensor {
pinctrl-names = “default”;
pinctrl-0 = <&dht22>;
compatible = “dht11-gpio”;
gpios = <&gpio3 19 0>;
};
At the bottom of the subsequent section (&am33xx_pinmux), I added:
dht22: dht22 {
pinctrl-single,pins = <
0x1a4 0x17 /* P9_27 */
;
};
My understanding is that this puts P9_27 (0x1a4) into mode 7 (GPIO) for output pullup. In talking with the driver developer, he said, “The point of my setup is to enable the internal pullup of the imx23 gpio line.” His device tree modifications (for imx23-olinuxino.dts) looked like:
dht22: dht22a@0 {
reg = <0>;
fsl,pinmux-ids = <
0x0073 /* MX23_PAD_GPMI_D07__GPIO_0_7 */
;
fsl,drive-strength = <0>;
fsl,voltage = <1>;
fsl,pull-up = <1>;
};
When I boot and load the driver module, I do see what should be the interface to the device: /sys/devices/humidity_sensor.8/iio:device0, but when I attempt to read from it, I get “Invalid argument.”
cat /sys/devices/humidity_sensor.8/iio:device0/in_temp_input
cat: /sys/devices/humidity_sensor.8/iio:device0/in_temp_input: Invalid argument
Does anyone with more device tree and BBB experience have any suggestions? I suspect I’m doing something stupid with that pin configuration… Any help would be greatly appreciated, thank you!