linux-kernel - Re: [PATCH v2] input: fix BTN_TOUCH reporting in input_mt_report_pointer

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Date:	Tue, 28 Oct 2014 14:07:06 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	Chung-yih Wang <cywang@...omium.org>,
	linux-input <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Henrik Rydberg <rydberg@...omail.se>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH v2] input: fix BTN_TOUCH reporting in
 input_mt_report_pointer_emulation

On Tue, Oct 28, 2014 at 04:47:56PM -0400, Benjamin Tissoires wrote:
> Hi Chung-yih,
> 
> On Mon, Oct 27, 2014 at 6:08 AM, Chung-yih Wang <cywang@...omium.org> wrote:
> >   From the definition of BTN_TOUCH, BTN_TOOL_<name> and BTN_TOUCH codes
> > are orthogonal. BTN_TOUCH should be zero if there is no physical contact
> > happened on device. With ABS_MT_DISTANCE information, the patch uses
> > touch_count and finger_count to get the final reporting code for
> > BTN_TOUCH and BTN_TOOL_<name>, respectively.
> >
> > Signed-off-by: Chung-yih Wang <cywang@...omium.org>
> > ---
> >  drivers/input/input-mt.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
> > index fbe29fc..a2ab8e3 100644
> > --- a/drivers/input/input-mt.c
> > +++ b/drivers/input/input-mt.c
> > @@ -192,18 +192,21 @@ void input_mt_report_pointer_emulation(struct input_dev *dev, bool use_count)
> >  {
> >         struct input_mt *mt = dev->mt;
> >         struct input_mt_slot *oldest;
> > -       int oldid, count, i;
> > +       int oldid, i;
> > +       int touch_count, finger_count;
> >
> >         if (!mt)
> >                 return;
> >
> >         oldest = NULL;
> >         oldid = mt->trkid;
> > -       count = 0;
> > +       touch_count = 0;
> > +       finger_count = 0;
> >
> >         for (i = 0; i < mt->num_slots; ++i) {
> >                 struct input_mt_slot *ps = &mt->slots[i];
> >                 int id = input_mt_get_value(ps, ABS_MT_TRACKING_ID);
> > +               int distance = input_mt_get_value(ps, ABS_MT_DISTANCE);
> 
> I don't really like this statement, even if it works. Some devices do
> not report ABS_MT_DISTANCE, and the value for them should not be
> considered as '0' but 'undefined'.

I think it incidentally still 0 as we zero out memory we allocate.

> 
> >
> >                 if (id < 0)
> >                         continue;
> > @@ -211,12 +214,14 @@ void input_mt_report_pointer_emulation(struct input_dev *dev, bool use_count)
> >                         oldest = ps;
> >                         oldid = id;
> >                 }
> > -               count++;
> > +               finger_count++;
> > +               if (distance == 0)
> 
> I'd rather test here if ABS_MT_DISTANCE is used, and then if the value is 0.
> 
> > +                       touch_count++;

I do not think we should include hovering contacts into finger_count
either. I.e if I have one finger touching and one finger hovering we
should be emitting BTN_TOOL_FINGER and not BTN_TOOL_DOUBLETAP.

> >         }
> >
> > -       input_event(dev, EV_KEY, BTN_TOUCH, count > 0);
> > +       input_event(dev, EV_KEY, BTN_TOUCH, touch_count > 0);
> 
> For the record, I *think* this will not break user space. This is used
> in the touchpad part of libinput, and does not seemed to be impacted
> by the change.
> Adding Peter and Hans in CC who can tell us if I am assuming right.
> 
> Cheers,
> Benjamin
> 
> >         if (use_count)
> > -               input_mt_report_finger_count(dev, count);
> > +               input_mt_report_finger_count(dev, finger_count);
> >
> >         if (oldest) {
> >                 int x = input_mt_get_value(oldest, ABS_MT_POSITION_X);
> > --
> > 2.1.2
> >

Thanks.

-- 
Dmitry
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