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Subject: RE: [PATCH v2 08/10] Input: elan_i2c - export true width/height
Date:   Mon, 27 May 2019 11:55:01 +0800
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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.

Cheers,
Benjamin


>
>         data->input = input;
>
> --
> 2.21.0
>