Re: [PATCH] Input: mt: only perform pointer emulation on drivers desiring this functionality

On Thu, Oct 27, 2016 at 4:54 PM, Dmitry Torokhov
[off-list ref] wrote:

On Thu, Oct 27, 2016 at 04:46:01PM -0700, Roderick Colenbrander wrote:

quoted

On Thu, Oct 27, 2016 at 4:19 PM, Dmitry Torokhov
[off-list ref] wrote:

quoted

On Thu, Oct 27, 2016 at 02:31:13PM -0700, Roderick Colenbrander wrote:

quoted

From: Roderick Colenbrander <roderick.colenbrander@sony.com>

The input-mt driver pointer emulation from 'input_mt_sync_frame' regardless
of the flags passed in to 'input_mt_init_slots' by device drivers.

Right, because needing single-touch (pointer) emulation is not property
of device or driver but rather consumer. If we get to the point where
everything is ready to accept multi-touch (are we there yet) then we can
stop doing pointer emulation altogether.

quoted

Pointer emulation is undesired on drivers, which didn't request this
capability like the hid-sony driver for the Dualshock 4. This gamepad already
reports ABS_X / ABS_Y for gamepad stick purposes. Pointer emulation would
inject touchpad values into these sticks, which is undesired.

The driver should not be re-purposing events like that.
ABS_MT_POSITION_X and ABS_X should match.

Why doesn't driver follow Documentation/input/gamepad.txt?

The original hid-sony code and the multitouch handling code for the Dualshock 4
were written by the community. We are stepping in to make the hid-sony driver
properly handle the Dualshock 4.
The driver doesn't fully follow the gamepad spec yet, which we will
try to improve. At
least the left analog stick is reported as ABS_X and ABS_Y already,
but the buttons
are inconsistent and right stick is wrong as well.
While it would be great to conform to the spec, the conflict with
multitouch would still
exist as the Dualshock 4 has both analog sticks and a multitouch touchpad.

Disabling the pointer emulation feature avoids the conflict. This
issue was only exposed
recently by adding of the input_mt_sync_frame call as recommended by Benjamin as
part of some improvements we did for touchpad handling in hid-sony.

As I mentioned, ABS_MT_POSITION_X and ABS_X should represent the same
data, so the driver's use of them for different sub-devices is not
correct. Maybe the multitouch "touchpad" should be reported as
completely separate input device and userspace should "stitch" it back
into composite device.

In any case, as I mentioned above, the pointer emulation is requirement
of client and thus this patch is not appropriate.

Thanks.

--
Dmitry

Thanks for your reply. I guess the only option then is to create an
actual sub device. I suppose
we are not the first input driver exposing sub devices. Are there good
example drivers you can
recommend (or drivers to avoid glancing at)?

The only concern I have is the stitching together in user space, which
not kinds of platforms
or userland libraries are handling. The only way is to inspect sysfs
and try to tie things together.
It would be nice if there was some better way. From memory Video4Linux
exposed various
APIs to locate subdevices from the 'master' device.

Thanks,
Roderick