mbox series

[RFC,0/2] Input: adc-joystick: add detachable devices support

Message ID 20221031190159.1341027-1-lis8215@gmail.com
Headers
Series Input: adc-joystick: add detachable devices support |

Message

Siarhei Volkau Oct. 31, 2022, 7:01 p.m. UTC 
  For detachable or lock-able joysticks the ADC lanes might
be biased to GND or AVDD when the joystick is detached/locked.

One such kind of joystick is found in the Ritmix RZX-50 handheld.
The joystick is non-detachable, although ADC lane biased to power
supply when the "Hold" switch is activated.

To avoid reporting old/broken measurements valid-range is introduced.
When measured value is outside valid-range the driver reports
safe center position for corresponding axis.

Siarhei Volkau (2):
  dt-bindings: adc-joystick: add valid-range
  Input: adc-joystick - add detachable devices support

 .../bindings/input/adc-joystick.yaml          | 62 +++++++++++++++++++
 drivers/input/joystick/adc-joystick.c         | 58 ++++++++++++++++-
 2 files changed, 119 insertions(+), 1 deletion(-)

Comments

Paul Cercueil Nov. 5, 2022, 11:39 p.m. UTC | #1 
Hi Siarhei,

Le lun. 31 oct. 2022 à 22:01:57 +0300, Siarhei Volkau 
<lis8215@gmail.com> a écrit :
> For detachable or lock-able joysticks the ADC lanes might
> be biased to GND or AVDD when the joystick is detached/locked.
> 
> One such kind of joystick is found in the Ritmix RZX-50 handheld.
> The joystick is non-detachable, although ADC lane biased to power
> supply when the "Hold" switch is activated.

But the RZX-50 has no joystick...
Or is the d-pad actually wired to the ADC instead of GPIOs?

> To avoid reporting old/broken measurements valid-range is introduced.
> When measured value is outside valid-range the driver reports
> safe center position for corresponding axis.

First of all, you already have a "valid range", it is called 
"abs-range"; no need for a new one.

Then, the driver has no business doing events filtering. Notice that 
when you activate the "hold" button and your joystick values go way 
off-range, you still get input events in userspace: that's because the 
kernel is not responsible for enforcing the deadzone, the userspace is.

In your case, you need to update your userspace applications/libraries 
so that when the joystick values are way off-range, the assumed 
position is the center.

Cheers,
-Paul
Siarhei Volkau Nov. 6, 2022, 8:47 a.m. UTC | #2 
вс, 6 нояб. 2022 г. в 02:39, Paul Cercueil <paul@crapouillou.net>:
>
> Hi Siarhei,
>
> Le lun. 31 oct. 2022 à 22:01:57 +0300, Siarhei Volkau
> <lis8215@gmail.com> a écrit :
> > For detachable or lock-able joysticks the ADC lanes might
> > be biased to GND or AVDD when the joystick is detached/locked.
> >
> > One such kind of joystick is found in the Ritmix RZX-50 handheld.
> > The joystick is non-detachable, although ADC lane biased to power
> > supply when the "Hold" switch is activated.
>
> But the RZX-50 has no joystick...

Well, actually there's two versions in the wild (google "RZX-50 pictures"):
 - with analog joystick and speakers on the back side
 - without the joystick and speakers on the front side
I have only the first one at the moment, but I'm looking for another one.

> Or is the d-pad actually wired to the ADC instead of GPIOs?

The D-Pad is another kind of pain there - it's a part of the matrix-keypad
but the pad's row line is shared with the LCD HSYNC signal.

> > To avoid reporting old/broken measurements valid-range is introduced.
> > When measured value is outside valid-range the driver reports
> > safe center position for corresponding axis.
>
> First of all, you already have a "valid range", it is called
> "abs-range"; no need for a new one.
>
> Then, the driver has no business doing events filtering. Notice that
> when you activate the "hold" button and your joystick values go way
> off-range, you still get input events in userspace: that's because the
> kernel is not responsible for enforcing the deadzone, the userspace is.
>
> In your case, you need to update your userspace applications/libraries
> so that when the joystick values are way off-range, the assumed
> position is the center.

Many userspace apps use SDL library to handle joystick input, the SDL
unfortunately hides the fact that the joystick position is out of range -
it does normalization and clamping of the abs-range to an int16_t range.

I see two approaches to do that in userspace:
1. Make a quirk in the SDL library, which affects many types of joysticks
and lead to a fragmentation (special userspace apps for every hardware
isn't the right way in my opinion).
2. Make a special filter app which will filter out invalid joystick events and
route rest to the /dev/input/uinput. Not sure how to hide the real joystick
device from libraries like SDL then.
Both of them don't look like a "silver bullet", however feasible.

>
> Cheers,
> -Paul
>
>

Thank you.
Siarhei Volkau Nov. 6, 2022, 3:22 p.m. UTC | #3 
> Not sure how to hide the real joystick device from libraries like SDL

Got it, EVIOCGRAB ioctl shall do the job.

Thank you all !

BR,
Siarhei