Re: [PATCH v2 08/10] Input: elan_i2c - export true width/height

[Harry Cutts <hcutts@chromium.org>]

On Mon, 27 May 2019 at 18:21, Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
>
> Hi Benjamin, KT,
>
> On Mon, May 27, 2019 at 11:55:01AM +0800, 廖崇榮 wrote:
> > Hi
> >
> > -----Original Message-----
> > From: Benjamin Tissoires [mailto:benjamin.tissoires@redhat.com]
> > Sent: Friday, May 24, 2019 5:37 PM
> > To: Dmitry Torokhov; KT Liao; Rob Herring; Aaron Ma; Hans de Goede
> > Cc: open list:HID CORE LAYER; lkml; devicetree@vger.kernel.org
> > Subject: Re: [PATCH v2 08/10] Input: elan_i2c - export true width/height
> >
> > On Tue, May 21, 2019 at 3:28 PM Benjamin Tissoires <benjamin.tissoires@redhat.com> wrote:
> > >
> > > The width/height is actually in the same unit than X and Y. So we
> > > should not tamper the data, but just set the proper resolution, so
> > > that userspace can correctly detect which touch is a palm or a finger.
> > >
> > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > >
> > > --
> > >
> > > new in v2
> > > ---
> > >  drivers/input/mouse/elan_i2c_core.c | 11 ++++-------
> > >  1 file changed, 4 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/input/mouse/elan_i2c_core.c
> > > b/drivers/input/mouse/elan_i2c_core.c
> > > index 7ff044c6cd11..6f4feedb7765 100644
> > > --- a/drivers/input/mouse/elan_i2c_core.c
> > > +++ b/drivers/input/mouse/elan_i2c_core.c
> > > @@ -45,7 +45,6 @@
> > >  #define DRIVER_NAME            "elan_i2c"
> > >  #define ELAN_VENDOR_ID         0x04f3
> > >  #define ETP_MAX_PRESSURE       255
> > > -#define ETP_FWIDTH_REDUCE      90
> > >  #define ETP_FINGER_WIDTH       15
> > >  #define ETP_RETRY_COUNT                3
> > >
> > > @@ -915,12 +914,8 @@ static void elan_report_contact(struct elan_tp_data *data,
> > >                         return;
> > >                 }
> > >
> > > -               /*
> > > -                * To avoid treating large finger as palm, let's reduce the
> > > -                * width x and y per trace.
> > > -                */
> > > -               area_x = mk_x * (data->width_x - ETP_FWIDTH_REDUCE);
> > > -               area_y = mk_y * (data->width_y - ETP_FWIDTH_REDUCE);
> > > +               area_x = mk_x * data->width_x;
> > > +               area_y = mk_y * data->width_y;
> > >
> > >                 major = max(area_x, area_y);
> > >                 minor = min(area_x, area_y); @@ -1123,8 +1118,10 @@
> > > static int elan_setup_input_device(struct elan_tp_data *data)
> > >                              ETP_MAX_PRESSURE, 0, 0);
> > >         input_set_abs_params(input, ABS_MT_TOUCH_MAJOR, 0,
> > >                              ETP_FINGER_WIDTH * max_width, 0, 0);
> > > +       input_abs_set_res(input, ABS_MT_TOUCH_MAJOR, data->x_res);
> > >         input_set_abs_params(input, ABS_MT_TOUCH_MINOR, 0,
> > >                              ETP_FINGER_WIDTH * min_width, 0, 0);
> > > +       input_abs_set_res(input, ABS_MT_TOUCH_MINOR, data->y_res);
> >
> > I had a chat with Peter on Wednesday, and he mentioned that this is dangerous as Major/Minor are max/min of the width and height. And given that we might have 2 different resolutions, we would need to do some computation in the kernel to ensure the data is correct with respect to the resolution.
> >
> > TL;DR: I don't think we should export the resolution there :(
> >
> > KT, should I drop the patch entirely, or is there a strong argument for keeping the ETP_FWIDTH_REDUCE around?
> > I suggest you apply the patch, I have no idea why ETP_FWIDTH_REDUCE existed.
> > Our FW team know nothing about ETP_FWIDTH_REDUCE ether.
> >
> > The only side effect will happen on Chromebook because such computation have stayed in ChromeOS' kernel for four years.
> > Chrome's finger/palm threshold may be different from other Linux distribution.
> > We will discuss it with Google once the patch picked by chrome and cause something wrong.
>
> Chrome has logic that contact with maximum major/minor is treated as a
> palm, so here the driver (which originally came from Chrome OS)
> artificially reduces the contact size to ensure that palm rejection
> logic does not trigger.
>
> I'm adding Harry to confirm whether we are still using this logic and to
> see if we can adjust it to be something else.

I'm not very familiar with our touchpad code, so adding Sean O'Brien, who is.