Re: Question regarding multitouch input on Linux kernel

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Hi Nuno,

On Mon, Feb 25, 2013 at 4:00 PM, Nuno Santos <nsantos@xxxxxxxxxxx> wrote:
> Hi,
>
> I have been experiencing an issue with a Linux driver for multitouch input
> that i'm responsible for maintaining.

Side note. Your driver does not seems to be upstreamed (or I missed
it). You should really consider put it upstream. If we make changes in
the multitouch API, we can change your driver too, whereas here, you
will have to maintain several releases of your driver, one per kernel
version.

>
> The issue is basically the following:
>
> - I load the driver and the mouse works just fine
> - I touch the screen and the first touch input is delivered to the system
> - On that very same moment I can't use mouse left button down to click on
> folders on nautilus. I can only selected them using drag select. I also
> can't get a folder to get selected with a single touch input.
> - The user experience with the mouse gets inconsistent.
> - Unloading the module doesn't return the good experience
> - Restarting X fixes the problem until I report a touch input again with
> this driver
> - If I only use common pointer input, the issue doesn't occur.
>
> My questions resides in if the problem is due to bad touch reporting, or due
> to a bug in X/nautilus.

Definitively X and nautilus problems. The very same kind of problems
were observed in Fedora 17 and fixed in the X.org shipped in Fedora
18.

Ubuntu is relying on an older X.org release, which contains several
bugs related to multitouch.

>
> I have been analyzing a lot of examples under kernel tree for multitouch
> input under Linux an it seems I'm doing what is necessary.
>
> I'm using Ubuntu 12.04 but this happened with Ubuntu 11.XX already

And in 12.10 also IIRC. I really hope that they will rebase X.org in 13.04.

>
> This what I do in order to declare device capabilities:
>
> input_set_abs_params(input_dev, ABS_X, 0, 6300, 0, 0);
> input_set_abs_params(input_dev, ABS_Y, 0, 6300, 0, 0);
>
> input_mt_init_slots(input_dev, DPX_TOUCH_MAX_COUNT);

input_mt_init_slots has been changed recently, it takes an extra arg: 'flags'.

> input_set_abs_params(input_dev, ABS_MT_POSITION_X, 0, 6300, 0, 0);
> input_set_abs_params(input_dev, ABS_MT_POSITION_Y, 0, 6300, 0, 0);

Not required IIRC. The params are copied from their single-touch equivalent.

>
> This is what I do in order to report touches:
>
> for (currentTouch=0;currentTouch<DPX_TOUCH_MAX_COUNT &&
> touchCount<priv->context->State.Acquisition.TouchPoints;++currentTouch)
>     {
>         Touch = priv->context->State.Touches + currentTouch;
>
>         x = Touch->CalibratedPoint.Position.X;
>         y = Touch->CalibratedPoint.Position.Y;
>
>         input_mt_slot(usbtouch->input, currentTouch);
>
>         // touch down
>         if(Touch->CurrentState==DPX_TOUCH_STATE_ACTIVE &&
> Touch->ReportedState==DPX_TOUCH_STATE_INACTIVE)
>         {
>             Touch->ReportedState = DPX_TOUCH_STATE_ACTIVE;
>
>             input_mt_report_slot_state(usbtouch->input, MT_TOOL_FINGER, 1);
>
>             input_report_abs(usbtouch->input, ABS_MT_POSITION_X, x);
>             input_report_abs(usbtouch->input, ABS_MT_POSITION_Y, y);
>
>             touchCount++;
>         }
>         // touch move
>         else if (Touch->CurrentState==DPX_TOUCH_STATE_ACTIVE &&
> Touch->ReportedState==DPX_TOUCH_STATE_ACTIVE)
>         {
>             Touch->ReportedState = DPX_TOUCH_STATE_ACTIVE;
>
>             input_mt_report_slot_state(usbtouch->input, MT_TOOL_FINGER, 1);
>
>             input_report_abs(usbtouch->input, ABS_MT_POSITION_X, x);
>             input_report_abs(usbtouch->input, ABS_MT_POSITION_Y, y);
>
>             touchCount++;
>         }
>         // touch up
>         else
>         {
>             Touch->ReportedState = DPX_TOUCH_STATE_INACTIVE;
>
>             input_mt_report_slot_state(usbtouch->input, MT_TOOL_FINGER, 0);
>
>             input_report_abs(usbtouch->input, ABS_MT_POSITION_X, x);
>             input_report_abs(usbtouch->input, ABS_MT_POSITION_Y, y);

No need to update ABS_MT_POSITION_X/Y in this case: they should not be
sent to the user space according to the multitouch protocol.

>
>             touchCount++;
>         }
>     }
>
>     if (touchCount>0)

Looks like this test is always true.

>     {
>         input_mt_report_pointer_emulation(usbtouch->input, true);

In the latest version of the kernel tree, you should rely on the
input_mt_sync_frame() now. It will call
input_mt_report_pointer_emulation() plus other things depending of the
flags you passed to input_mt_init_slots().

>         input_sync(usbtouch->input);
>     }
>
>

Cheers,
Benjamin
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