linux-kernel - Re: [PATCH] CHROMIUM: Input: synaptics - filter out the events with low z values

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Message-ID: <20120222083858.GA26570@polaris.bitmath.org>
Date:	Wed, 22 Feb 2012 09:38:58 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Chung-yih Wang <cywang@...omium.org>
Cc:	Alessandro Rubini <rubini@...vis.unipv.it>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	djkurtz@...omium.org
Subject: Re: [PATCH] CHROMIUM: Input: synaptics - filter out the events with
 low z values

Hi Chung-yih Wang,

> The single touch path imposes a minimum z value (with hysterisis) before
> registering BTN_TOUCH. Apply the same (hard coded) threshold when
> deciding how many fingers to report in the semi-mt path.
> 
> This patch improves performance of the Google Cr-48 chromebook's
> extremely sensitive Synaptics profile sensor touchpad by filtering out
> touch events for hovering fingers.
> 
> Note: We continue to use the same hard coded threshold value used in the
> single touch case as it appears this works just as well on these
> multitouch profile sensor pads as on whatever pads it was originally
> discovered.
> 
> Signed-off-by: Chung-Yih Wang <cywang@...omium.org>
> ---

The idea is sound and has worked well in practise for a long
time. However, please see the comments inline.

>  drivers/input/mouse/synaptics.c |   15 +++++++++++----
>  1 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
> index 8081a0a..746dbcc 100644
> --- a/drivers/input/mouse/synaptics.c
> +++ b/drivers/input/mouse/synaptics.c
> @@ -568,17 +568,22 @@ static void synaptics_report_semi_mt_slot(struct input_dev *dev, int slot,
>  	}
>  }
>  
> +static bool finger_touched(const struct synaptics_hw_state *hw)
> +{
> +	return (hw->z > 30);
> +}
> +
>  static void synaptics_report_semi_mt_data(struct input_dev *dev,
>  					  const struct synaptics_hw_state *a,
>  					  const struct synaptics_hw_state *b,
>  					  int num_fingers)
>  {
> -	if (num_fingers >= 2) {
> +	if ((num_fingers >= 2) && finger_touched(a) && finger_touched(b)) {
>  		synaptics_report_semi_mt_slot(dev, 0, true, min(a->x, b->x),
>  					      min(a->y, b->y));
>  		synaptics_report_semi_mt_slot(dev, 1, true, max(a->x, b->x),
>  					      max(a->y, b->y));
> -	} else if (num_fingers == 1) {
> +	} else if ((num_fingers == 1) && finger_touched(a)) {
>  		synaptics_report_semi_mt_slot(dev, 0, true, a->x, a->y);
>  		synaptics_report_semi_mt_slot(dev, 1, false, 0, 0);
>  	} else {

So if num_fingers == 2 and only one of a and b returns
finger_touched() == true, we fall back to zero fingers?

> @@ -1040,8 +1045,10 @@ static void synaptics_process_packet(struct psmouse *psmouse)
>  	 * BTN_TOUCH has to be first as mousedev relies on it when doing
>  	 * absolute -> relative conversion
>  	 */
> -	if (hw.z > 30) input_report_key(dev, BTN_TOUCH, 1);
> -	if (hw.z < 25) input_report_key(dev, BTN_TOUCH, 0);
> +	if (finger_touched(&hw))
> +		input_report_key(dev, BTN_TOUCH, 1);
> +	if (hw.z < 25)
> +		input_report_key(dev, BTN_TOUCH, 0);
>  
>  	if (num_fingers > 0) {
>  		input_report_abs(dev, ABS_X, hw.x);

Why not introduce hysteresis for all fingers here? There is an example
implementation in bcm5974.c in the same directory.

Thanks,
Henrik
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