On Wed, Feb 22, 2012 at 4:38 PM, Henrik Rydberg [off-list ref] wrote:

Hi Chung-yih Wang,

quoted

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 <redacted>
---

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

quoted

 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?

Actually, yes.   In this case, we will have 2 x's and 2 y's, but not
know which belong to a good finger and which belong to a too light
finger....  sigh... synaptics... sigh...

quoted

@@ -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.

Good idea, can it be in a different, follow-up patch?

Thanks,
Henrik