iio A/D converter input to input event subsystem

iio A/D converter input to input event subsystem

[gmane]

Hi,

I would like to use a couple of resistors and keys and one Analog 
input[1], read the analogue voltage from a kernel driver, figure out 
which key is pressed and pass this on to the Linux input subsystem. (Am 
I really the only one with this use case?)

In my specific case it's about a beagle bone black, which means that the 
A/D driver is an iio adc driver[2].

How would it be possible to reuse the iio A/D converter driver code for 
my driver? Maybe it would even be possible to create something more 
generic so iio A/D converter channels could be used as input keys. Some 
sample code which would enable me to choose an analog input and read 
from it from kernel space would help me to write some basic sample 
driver, I guess.

The reason I would like to write a device driver instead of a user space 
application is mainly the input subsystem. From the user space 
application's point of view utilizing a device driver which feeds the 
input subsystem would make it easy to exchange what's underneath without 
user space even noticing. (keys to Input pins, a key matrix to I/O pins, 
i2c input, A/D converter,...).

Regards,

Robert

[1] 
http://21stdigitalhome.blogspot.gr/2013/11/sensing-switches-on-analog-input.html
[2] 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iio/adc/ti_am335x_adc.c?id=refs/tags/v3.16-rc7

Re: iio A/D converter input to input event subsystem

[Alexandre Belloni]

Hi Robert,

On 02/08/2014 at 13:14:30 -0500, gmane@reliableembeddedsystems.com wrote :
> Hi,
> 
> I would like to use a couple of resistors and keys and one Analog
> input[1], read the analogue voltage from a kernel driver, figure out
> which key is pressed and pass this on to the Linux input subsystem.
> (Am I really the only one with this use case?)
> 
> In my specific case it's about a beagle bone black, which means that
> the A/D driver is an iio adc driver[2].
> 
> How would it be possible to reuse the iio A/D converter driver code
> for my driver? Maybe it would even be possible to create something
> more generic so iio A/D converter channels could be used as input
> keys. Some sample code which would enable me to choose an analog
> input and read from it from kernel space would help me to write some
> basic sample driver, I guess.
> 
> The reason I would like to write a device driver instead of a user
> space application is mainly the input subsystem. From the user space
> application's point of view utilizing a device driver which feeds
> the input subsystem would make it easy to exchange what's underneath
> without user space even noticing. (keys to Input pins, a key matrix
> to I/O pins, i2c input, A/D converter,...).
> 

Did you have a look at uinput? This would allow you to inject input
events after processing the ADC values in userspace.

Simple example: http://thiemonge.org/getting-started-with-uinput

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Re: iio A/D converter input to input event subsystem

[gmane]

Hi,

On 2014-08-03 04:56, Alexandre Belloni wrote:
> Hi Robert,

> 
> Did you have a look at uinput? This would allow you to inject input
> events after processing the ADC values in userspace.
> 
> Simple example: http://thiemonge.org/getting-started-with-uinput

Thanks this looks interesting. I had in the meantime a look at iio_hwmon 
[1] which does something similar to what I want for the hwmon subsystem 
instead of the input event subsystem.

Regards,

Robert

[1] 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/hwmon/iio_hwmon.c?id=refs/tags/v3.16-rc7

Re: iio A/D converter input to input event subsystem

[Jonathan Cameron]

On 03/08/14 16:08, gmane@reliableembeddedsystems.com wrote:
> Hi,
> 
> On 2014-08-03 04:56, Alexandre Belloni wrote:
>> Hi Robert,
> 
>>
>> Did you have a look at uinput? This would allow you to inject input
>> events after processing the ADC values in userspace.
>>
>> Simple example: http://thiemonge.org/getting-started-with-uinput
> 
> Thanks this looks interesting. I had in the meantime a look at iio_hwmon [1] which does something similar to what I want
> for the hwmon subsystem instead of the input event subsystem.

There is a rather aged iio_input driver, that uses the buffered interface (not polled)
and could probably be adapted to your usecase reasonably easily.  The case is different enough
that I'd probably suggest a new driver for it though rather than trying to blugeon it into
the existing driver.

http://www.spinics.net/lists/linux-iio/msg06881.html (latest version I think).
The infrastructure for this went in back then, but the input driver never quite got the
attention it needed.

One big issue outstanding around this stuff is that no one likes the device
tree bindings.  Probably doesn't matter for your project in the short term however!

Jonathan
> 
> Regards,
> 
> Robert
> 
> [1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/hwmon/iio_hwmon.c?id=refs/tags/v3.16-rc7
=

Re: iio A/D converter input to input event subsystem

[gmane]

Hi,

On 2014-08-03 10:43, Jonathan Cameron wrote:
> 
> http://www.spinics.net/lists/linux-iio/msg06881.html (latest version I 
> think).
> The infrastructure for this went in back then, but the input driver
> never quite got the
> attention it needed.

Thanks!

I'll try to have some hardware prototype by end of August and will see 
if I can get my stuff to work as Alexandre suggested.

Ideally I'll try to cook up something similar to your iio_input stuff.

Which mainline kernel version would you suggest?
3.14 or 3.16?

Regards,

Robert

Re: iio A/D converter input to input event subsystem

[Jonathan Cameron]

On 03/08/14 17:39, gmane@reliableembeddedsystems.com wrote:
> Hi,
> 
> On 2014-08-03 10:43, Jonathan Cameron wrote:
>>
>> http://www.spinics.net/lists/linux-iio/msg06881.html (latest version I think).
>> The infrastructure for this went in back then, but the input driver
>> never quite got the
>> attention it needed.
> 
> Thanks!
> 
> I'll try to have some hardware prototype by end of August and will see if I can get my stuff to work as Alexandre
> suggested.
> 
> Ideally I'll try to cook up something similar to your iio_input stuff.
> 
> Which mainline kernel version would you suggest?
> 3.14 or 3.16?
Always as recent as possible.  Anything else makes getting support
from anyone tricky as no one can remember how it used to work :)

Jonathan
> 
> Regards,
> 
> Robert
> 
> 
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