Hi Dmitry,
Le mardi 19 décembre 2023 à 12:32 -0800, Dmitry Torokhov a écrit :
> On Fri, Dec 15, 2023 at 12:19:51PM +0100, Artur Rojek wrote:
> > On 2023-12-15 03:40, Chris Morgan wrote:
> > > From: Chris Morgan <macromorgan@xxxxxxxxxxx>
> > >
> > > uinput refuses to work with abs devices where the min value is
> > > greater
> > > than the max value. uinput_validate_absinfo() returns -EINVAL if
> > > this
> > > is the case and prevents using uinput on such a device. Since
> > > uinput
> > > has worked this way since at least kernel 2.6 (or prior) I
> > > presume that
> > > this is the correct way of doing things, and that this
> > > documentation
> > > needs to be clarified that min must always be less than max.
> > >
> > > uinput is used in my use case to bind together adc-joystick
> > > devices
> > > with gpio-keys devices to create a single unified gamepad for
> > > userspace.
> > >
> > > Note that there are several boards that will need to be
> > > corrected,
> > > all but a few of them I maintain. Submitting as an RFC for now to
> > > get
> > > comments from the input team and the original author in case
> > > there is
> > > something I am missing.
> > >
> > > Fixes: 7956b0d4694f ("dt-bindings: input: Add docs for ADC driven
> > > joystick")
> > >
> > > Signed-off-by: Chris Morgan <macromorgan@xxxxxxxxxxx>
> > > ---
> > > Documentation/devicetree/bindings/input/adc-joystick.yaml | 5
> > > +++--
> > > 1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/input/adc-
> > > joystick.yaml
> > > b/Documentation/devicetree/bindings/input/adc-joystick.yaml
> > > index 6c244d66f8ce..8f5cdd5ef190 100644
> > > --- a/Documentation/devicetree/bindings/input/adc-joystick.yaml
> > > +++ b/Documentation/devicetree/bindings/input/adc-joystick.yaml
> > > @@ -73,8 +73,9 @@ patternProperties:
> > > description: >
> > > Minimum and maximum values produced by the axis.
> > > For an ABS_X axis this will be the left-most and
> > > right-most
> > > - inclination of the joystick. If min > max, it is left
> > > to
> > > userspace to
> > > - treat the axis as inverted.
> > > + inclination of the joystick. The axis must always be
> > > expressed as
> > > + min < max, if the axis is inverted it is left to
> > > userspace to
> > > handle
> > > + the inversion.
> >
> > Hi Chris,
> >
> > Device Tree is supposed to depict the actual state of the hardware.
> > I worded the adc-joytick's adc-range property specifically, so that
> > it
> > covers a case of GCW Zero hardware [1], which has a joystick,
> > where the
> > ABS_X axis reports increasing values for the left-wards inclination
> > of
> > the joystick, and decreasing values for the right-wards
> > inclination. You
> > are saying that there are even more boards that need to be
> > corrected -
> > those are all situations, where DT depicts the actual behavior of
> > the
> > hardware.
> > What you are trying to do is change hardware description, because
> > of how
> > a driver in an OS works. You should instead fix behavior of said
> > driver,
> > even if nobody stumbled upon that issue since 2.6 :) We fixed
> > libSDL [2]
> > for the same reason.
>
> We have several places in the kernel (such as mousedev and joydev)
> where
> we expect that max is greater or equal to min if they are specified.
> I
> am sure that at least some userspace components also have this
> assumption. In general, we expect min to be a minimum value reported
> and
> max being maximum value reported, and orientation expressed via
> different properties (see [1]).
You can express all you want in DT properties the orientation of the
axis, it does not carry to userspace. As far as I can see there is
absolutely no way to tell userspace that an axis is inverted.
Cheers,
-Paul
>
> Since we codified min > max as inversion for adc-joystick devices in
> the
> bindings, I think we need to handle this *in that driver* and leave
> the
> rest alone.
>
> [1]
> Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml
>
> Thanks.
>
