how do I enable LRADC 0 in the i.MX28? I have the driver built into the kernel but I do not see the ii0 device

[tylerarnold]

I am trying to use the LRADC channel 0  on a Linux system using the i.MX28. I have the LRAD driver enabled in the kernel config and confirmed it in the modules.builtin. However when I look at the /sys/bus/iio/devices I do not see any devices. What additional configuration do I have to do to get the channel to work? Do I need to add the channels to the DTB ? I suspect so.

thanks!

-Tyler

[fabio_estevam]

On my mx28evk I can read the voltages like this:

root@freescale /$ cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

4095 

You can look at the imx28-evk.dts as a reference.

[tylerarnold]

yeah I have nothing there, and my dts is modeled after the imx28-evk and is pretty similar. I will double check everything though.

[fabio_estevam · Accepted solution]

On imx28-evk.dts we use the LRADC to provide touchscreen functionality:

		lradc@80050000 {
			fsl,lradc-touchscreen-wires = <4>;
			status = "okay";
			fsl,lradc-touchscreen-wires = <4>;
			fsl,ave-ctrl = <4>;
			fsl,ave-delay = <2>;
			fsl,settling = <10>;
		};

[tylerarnold]

is that DTS the one your board is actually using? I am looking at mxs-lradc.txt and it suggests entries like:

lradc@80050000 {

                compatible = "fsl,imx28-lradc";

                reg = <0x80050000 0x2000>;

                interrupts = <10 14 15 16 17 18 19 20 21 22 23 24 25>;

                status = "okay";

                fsl,lradc-touchscreen-wires = <5>;

                fsl,ave-ctrl = <4>;

                fsl,ave-delay = <2>;

                fsl,settling = <10>;

        };

the reg and interrupts are missing.

[fabio_estevam]

reg and interrupts are inside imx28.dtsi, which is included by imx28-evk.dts.

[tylerarnold]

yes, my lradc entry is identical.

[tylerarnold]

what kernel version are you building for? (I have 3.10.20 running)

[fabio_estevam]

I tried 3.18-rc5.

[tylerarnold]

my uboot environment was crusty/old, it was point at an old dtb which had the lrad registers disabled. I updated it to point to the new one I thought it was already using and channel 0 appears. Thanks for your help!

# cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3393

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3397

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3398

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3397

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3399

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3400

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3395

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3394

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3394

/ # cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

3395

[fabio_estevam]

Great! Please mark the answer as 'useful' or 'correct' then.