ALPS Trackpoint & pressure

ALPS Trackpoint & pressure

[Pali Rohár]

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Hi! Now playing again with trackpoint connected to ALPS rushmore
touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
reports pressure of trackpoint. Parser for it is already implemented in
alps.c and value is assigned to variable "z". When I just move
trackpoint z is zero, when I push trackpoint while moving, then z is
number higher, maximally 32. Variable "z" is set, but unused.

Do we have some input interface which can be used to report this
pressure of trackpoint to userspace? I can use this feature e.g. as
additional button...

-- 
Pali Rohár
pali.rohar@gmail.com

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Re: ALPS Trackpoint & pressure

[Dmitry Torokhov]

On Sun, Feb 04, 2018 at 04:08:39PM +0100, Pali Rohár wrote:
> Hi! Now playing again with trackpoint connected to ALPS rushmore
> touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
> reports pressure of trackpoint. Parser for it is already implemented in
> alps.c and value is assigned to variable "z". When I just move
> trackpoint z is zero, when I push trackpoint while moving, then z is
> number higher, maximally 32. Variable "z" is set, but unused.
> 
> Do we have some input interface which can be used to report this
> pressure of trackpoint to userspace? I can use this feature e.g. as
> additional button...

We could either do the conversion in kernel and emit BTN_LEFT, or
report ABS_PRESSURE and see if userspace will be able to handle
REL_X/REL_Y/ABS_PRESSURE device.

Adding Peter.

-- 
Dmitry

Re: ALPS Trackpoint & pressure

[Peter Hutterer]

On Mon, Feb 05, 2018 at 02:49:55PM -0800, Dmitry Torokhov wrote:
> On Sun, Feb 04, 2018 at 04:08:39PM +0100, Pali Rohár wrote:
> > Hi! Now playing again with trackpoint connected to ALPS rushmore
> > touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
> > reports pressure of trackpoint. Parser for it is already implemented in
> > alps.c and value is assigned to variable "z". When I just move
> > trackpoint z is zero, when I push trackpoint while moving, then z is
> > number higher, maximally 32. Variable "z" is set, but unused.
> > 
> > Do we have some input interface which can be used to report this
> > pressure of trackpoint to userspace? I can use this feature e.g. as
> > additional button...
> 
> We could either do the conversion in kernel and emit BTN_LEFT, or
> report ABS_PRESSURE and see if userspace will be able to handle
> REL_X/REL_Y/ABS_PRESSURE device.
> 
> Adding Peter.

judging by trackpoint history, I'd leave the pressure->click conversion to
userspace because every trackpoint may need a different threshold setting.
"easier" to have this in userspace with dmi matches etc. plus, converting to
BTN_LEFT in the kernel means we cannot use it as a separate interaction
anymore.

That aside, I think exporting ABS_PRESSURE is fine, that's what it's there
for. Nothing will use it for now though, tbh not sure yet how that would be
exported from libinput. but worth filing a bug for, please assign it to me.

Cheers,
   Peter

Re: ALPS Trackpoint & pressure

[Pali Rohár]

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On Tuesday 06 February 2018 10:29:47 Peter Hutterer wrote:
> On Mon, Feb 05, 2018 at 02:49:55PM -0800, Dmitry Torokhov wrote:
> > On Sun, Feb 04, 2018 at 04:08:39PM +0100, Pali Rohár wrote:
> > > Hi! Now playing again with trackpoint connected to ALPS rushmore
> > > touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
> > > reports pressure of trackpoint. Parser for it is already implemented in
> > > alps.c and value is assigned to variable "z". When I just move
> > > trackpoint z is zero, when I push trackpoint while moving, then z is
> > > number higher, maximally 32. Variable "z" is set, but unused.
> > > 
> > > Do we have some input interface which can be used to report this
> > > pressure of trackpoint to userspace? I can use this feature e.g. as
> > > additional button...
> > 
> > We could either do the conversion in kernel and emit BTN_LEFT, or
> > report ABS_PRESSURE and see if userspace will be able to handle
> > REL_X/REL_Y/ABS_PRESSURE device.
> > 
> > Adding Peter.
> 
> judging by trackpoint history, I'd leave the pressure->click conversion to
> userspace because every trackpoint may need a different threshold setting.
> "easier" to have this in userspace with dmi matches etc. plus, converting to
> BTN_LEFT in the kernel means we cannot use it as a separate interaction
> anymore.

Also BTN_LEFT is already reported when left button under trackpoint is
pressed. Therefore it would not be possible to distinguish between
trackpoint "press" and real left button press.

> That aside, I think exporting ABS_PRESSURE is fine, that's what it's there
> for. Nothing will use it for now though, tbh not sure yet how that would be
> exported from libinput. but worth filing a bug for, please assign it to me.

Ok, so ABS_PRESSURE? Also then question is, how to report minimal and
maximal (possible) value? If we are going to "standardize" API for it,
we should also define min/max values, so userspace would be able to
normalize this pressure event. I can imagine that some devices can
report 8bit value, but ALPS rushmore reports only 5bit value.

-- 
Pali Rohár
pali.rohar@gmail.com

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Re: ALPS Trackpoint & pressure

[Peter Hutterer]

On Fri, Feb 09, 2018 at 12:21:41AM +0100, Pali Rohár wrote:
> On Tuesday 06 February 2018 10:29:47 Peter Hutterer wrote:
> > On Mon, Feb 05, 2018 at 02:49:55PM -0800, Dmitry Torokhov wrote:
> > > On Sun, Feb 04, 2018 at 04:08:39PM +0100, Pali Rohár wrote:
> > > > Hi! Now playing again with trackpoint connected to ALPS rushmore
> > > > touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
> > > > reports pressure of trackpoint. Parser for it is already implemented in
> > > > alps.c and value is assigned to variable "z". When I just move
> > > > trackpoint z is zero, when I push trackpoint while moving, then z is
> > > > number higher, maximally 32. Variable "z" is set, but unused.
> > > > 
> > > > Do we have some input interface which can be used to report this
> > > > pressure of trackpoint to userspace? I can use this feature e.g. as
> > > > additional button...
> > > 
> > > We could either do the conversion in kernel and emit BTN_LEFT, or
> > > report ABS_PRESSURE and see if userspace will be able to handle
> > > REL_X/REL_Y/ABS_PRESSURE device.
> > > 
> > > Adding Peter.
> > 
> > judging by trackpoint history, I'd leave the pressure->click conversion to
> > userspace because every trackpoint may need a different threshold setting.
> > "easier" to have this in userspace with dmi matches etc. plus, converting to
> > BTN_LEFT in the kernel means we cannot use it as a separate interaction
> > anymore.
> 
> Also BTN_LEFT is already reported when left button under trackpoint is
> pressed. Therefore it would not be possible to distinguish between
> trackpoint "press" and real left button press.

yep, that's what I meant with "we cannot use it as separate interaction",
we'd have no way to know how the click was generated.

> 
> > That aside, I think exporting ABS_PRESSURE is fine, that's what it's there
> > for. Nothing will use it for now though, tbh not sure yet how that would be
> > exported from libinput. but worth filing a bug for, please assign it to me.
> 
> Ok, so ABS_PRESSURE? Also then question is, how to report minimal and
> maximal (possible) value? If we are going to "standardize" API for it,
> we should also define min/max values, so userspace would be able to
> normalize this pressure event. I can imagine that some devices can
> report 8bit value, but ALPS rushmore reports only 5bit value.

tbh, I'm not putting my hopes on this being an accurate range ever. So
what's likely going to happen is that you pick a best-guess min/max for the
kernel and then we have dmi-based overrides for every single trackpoint in
userspace to tell us what a realistic threshold value for a click is and
what the actual min/max ranges is.

This is relatively easy to measure in userspace, we can pop it into
60-evdev.hwdb to override the min/max and ship the threshold values as
libinput-specific files. It's awful, but most likely the best we can do.

But hey, at least a min of 0 will be accurate ;)

Cheers,
   Peter

Re: ALPS Trackpoint & pressure

[Pali Rohár]

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On Friday 09 February 2018 09:57:03 Peter Hutterer wrote:
> On Fri, Feb 09, 2018 at 12:21:41AM +0100, Pali Rohár wrote:
> > On Tuesday 06 February 2018 10:29:47 Peter Hutterer wrote:
> > > On Mon, Feb 05, 2018 at 02:49:55PM -0800, Dmitry Torokhov wrote:
> > > > On Sun, Feb 04, 2018 at 04:08:39PM +0100, Pali Rohár wrote:
> > > > > Hi! Now playing again with trackpoint connected to ALPS rushmore
> > > > > touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
> > > > > reports pressure of trackpoint. Parser for it is already implemented in
> > > > > alps.c and value is assigned to variable "z". When I just move
> > > > > trackpoint z is zero, when I push trackpoint while moving, then z is
> > > > > number higher, maximally 32. Variable "z" is set, but unused.
> > > > > 
> > > > > Do we have some input interface which can be used to report this
> > > > > pressure of trackpoint to userspace? I can use this feature e.g. as
> > > > > additional button...
> > > > 
> > > > We could either do the conversion in kernel and emit BTN_LEFT, or
> > > > report ABS_PRESSURE and see if userspace will be able to handle
> > > > REL_X/REL_Y/ABS_PRESSURE device.
> > > > 
> > > > Adding Peter.
> > > 
> > > judging by trackpoint history, I'd leave the pressure->click conversion to
> > > userspace because every trackpoint may need a different threshold setting.
> > > "easier" to have this in userspace with dmi matches etc. plus, converting to
> > > BTN_LEFT in the kernel means we cannot use it as a separate interaction
> > > anymore.
> > 
> > Also BTN_LEFT is already reported when left button under trackpoint is
> > pressed. Therefore it would not be possible to distinguish between
> > trackpoint "press" and real left button press.
> 
> yep, that's what I meant with "we cannot use it as separate interaction",
> we'd have no way to know how the click was generated.
> 
> > 
> > > That aside, I think exporting ABS_PRESSURE is fine, that's what it's there
> > > for. Nothing will use it for now though, tbh not sure yet how that would be
> > > exported from libinput. but worth filing a bug for, please assign it to me.
> > 
> > Ok, so ABS_PRESSURE? Also then question is, how to report minimal and
> > maximal (possible) value? If we are going to "standardize" API for it,
> > we should also define min/max values, so userspace would be able to
> > normalize this pressure event. I can imagine that some devices can
> > report 8bit value, but ALPS rushmore reports only 5bit value.
> 
> tbh, I'm not putting my hopes on this being an accurate range ever. So
> what's likely going to happen is that you pick a best-guess min/max for the
> kernel and then we have dmi-based overrides for every single trackpoint in
> userspace to tell us what a realistic threshold value for a click is and
> what the actual min/max ranges is.
> 
> This is relatively easy to measure in userspace, we can pop it into
> 60-evdev.hwdb to override the min/max and ship the threshold values as
> libinput-specific files. It's awful, but most likely the best we can do.
> 
> But hey, at least a min of 0 will be accurate ;)
> 
> Cheers,
>    Peter

Now I see that alps.c already has following initialization code for
tracksticks:

		if (priv->flags & ALPS_DUALPOINT_WITH_PRESSURE) {
			input_set_capability(dev2, EV_ABS, ABS_PRESSURE);
			input_set_abs_params(dev2, ABS_PRESSURE, 0, 127, 0, 0);
		}

And for ALPS SS4 S2 devices alps.c sets that flag. And in function
alps_process_packet_ss4_v2() for SS4_PACKET_ID_STICK it calls:

		input_report_rel(dev2, REL_X, SS4_TS_X_V2(packet));
		input_report_rel(dev2, REL_Y, SS4_TS_Y_V2(packet));
		input_report_abs(dev2, ABS_PRESSURE, SS4_TS_Z_V2(packet));

Therefore ABS_PRESSURE is already used for one trackstick device.

I will prepare patch to export "z" axes also for other ALPS trackpoints
via that ABS_PRESSURE attribute.

Above input_set_abs_params() call already sets minimal and maximal
value, therefore this problem is solved too.

-- 
Pali Rohár
pali.rohar@gmail.com

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