Re: Reading ADC that comes from a multiplexer

[Peter Rosin <peda@axentia.se>]

On 2021-09-22 13:37, Fabio Estevam wrote:
> Hi Peter,
> 
> On Wed, Sep 22, 2021 at 4:27 AM Peter Rosin <peda@axentia.se> wrote:
> 
>> Basically, the whole point is that you simply don't. The iio-mux exposes
>> the channels as 8 new ADCs, and whenever you read a value from one of
>> them, the iio-mux operates the gpios for you, giving you the impression
>> that you have 8 independet ADCs. They are of course not independent, but...
> 
> Thanks for the clarification. It was helpful.
> 
>> That's exposed to user-space as:
>>
>> $ ls "/sys/bus/iio/devices/iio:device3"
>> in_altvoltage2_compare_interval  in_altvoltage5_scale
>> in_altvoltage2_invert            in_altvoltage6_compare_interval
>> in_altvoltage2_raw               in_altvoltage6_invert
>> in_altvoltage2_scale             in_altvoltage6_raw
>> in_altvoltage3_compare_interval  in_altvoltage6_scale
>> in_altvoltage3_invert            in_altvoltage7_compare_interval
>> in_altvoltage3_raw               in_altvoltage7_invert
>> in_altvoltage3_scale             in_altvoltage7_raw
>> in_altvoltage4_compare_interval  in_altvoltage7_scale
>> in_altvoltage4_invert            name
>> in_altvoltage4_raw               of_node
>> in_altvoltage4_scale             power
>> in_altvoltage5_compare_interval  subsystem
>> in_altvoltage5_invert            uevent
>> in_altvoltage5_raw
>> $ cat "/sys/bus/iio/devices/iio:device3/name"
>> envelope-detector-mux
> 
> Ah, so that's my issue then. I don't see a new device inside
> /sys/bus/iio/devices/.
> 
> I only see the original stmpe ADC:
> 
> ls "/sys/bus/iio/devices/iio:device0"
> dev              in_voltage5_raw  in_voltage_scale  power
> in_temp8_input   in_voltage6_raw  name              subsystem
> in_voltage4_raw  in_voltage7_raw  of_node           uevent
> 
> Maybe my dts is not correct to make the mux appear under
> /sys/bus/iio/devices/iio:device1.
> 
> Here is my dts that shows more context with the STMPE811 ADC:
> https://pastebin.com/raw/7Nn2aAtN
> 
> stmpe811 is an mfd device that can be used as a touchscreen and as a normal adc.
> 
> I only use the adc functionality.
> 
> Any suggestions are welcome.

Don't you get any output from the iio-mux driver during probe? I'd expect
a "failed to get parent channel" or something like that?

I don't know, but looking around a bit makes me think you should
investigate /arch/arm/boot/dts/am5729-beagleboneai.dts and/or
/arch/arm/boot/dts/exynos4412-p4note.dtsi.

I think you need to move the adc: label in the dts to the stmpe_adc child
node, or something like that?

Cheers,
Peter