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

On Thu, Oct 27, 2016 at 4:19 PM, Dmitry Torokhov
<dmitry.torokhov@xxxxxxxxx> wrote:

quoted

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

quoted

From: Roderick Colenbrander <redacted>

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.

The button and axis mappings are what the controller’s default HID descriptor provides.  The descriptors in the driver just extend the ones sent by the controller to allow additional functionality(i.e. gyro/accel and full Bluetooth mode), but the button and axis mappings were unchanged from the defaults so as not to introduce mapping discrepencies with older kernels which used the generic HID driver.  Note that changing them at this point *will* break a lot of software (SDL has had these mappings hardcoded into it’s controller database header for years now).

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.

Is input_mt_sync_frame even necessary?  The original implementation followed the protocol for a “Type B” device as defined in Documentation/input/multi-touch-protocol.txt which doesn’t require SYN_MT_REPORT messages.