Input: appletouch - verious updates for MacBooks

Change a bit the finger detection method used by the appletouch
driver to reduce touchpad "jumpiness":

 - Adjust the method for detecting multiple fingers. Previously, it
   recognized a new finger when a low sensor reading is followed by
   a high sensor reading. The new method checks for 'humps' in the
   sensor readings, so there doesn't necessarily have to be a low
   sensor between two high sensors for two fingers to be triggered.
   This allows detecting presence of two fingers on the touchpad
   even when they touch each other.

 - Change absolute coordinate calculation to us to get rid of "jumps".
   Instead of using full value from a sensor once it passes the
   threshold subtract theshold value from the reading.

 - Allow adjusting threshold value via module parameter.

The patch doesn't seem to affect the Powerbooks but does greatly improve
the touchpad behaviour on the MacBooks.

Signed-off-by: Jason Parekh <jasonparekh@gmail.com>
Signed-off-by: Stelian Pop <stelian@popies.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

diff --git a/drivers/usb/input/appletouch.c b/drivers/usb/input/appletouch.c
index 4c21351..4825db4 100644 (file)
--- a/drivers/usb/input/appletouch.c
+++ b/drivers/usb/input/appletouch.c
@@ -154,6 +154,13 @@ MODULE_AUTHOR("Johannes Berg, Stelian Pop, Frank Arnold, Michael Hanselmann");
 MODULE_DESCRIPTION("Apple PowerBooks USB touchpad driver");
 MODULE_LICENSE("GPL");
 
+/*
+ * Make the threshold a module parameter
+ */
+static int threshold = ATP_THRESHOLD;
+module_param(threshold, int, 0644);
+MODULE_PARM_DESC(threshold, "Discards any change in data from a sensor (trackpad has hundreds of these sensors) less than this value");
+
 static int debug = 1;
 module_param(debug, int, 0644);
 MODULE_PARM_DESC(debug, "Activate debugging output");
@@ -183,16 +190,48 @@ static int atp_calculate_abs(int *xy_sensors, int nb_sensors, int fact,
        int i;
        /* values to calculate mean */
        int pcum = 0, psum = 0;
+       int is_increasing = 0;
 
        *fingers = 0;
 
        for (i = 0; i < nb_sensors; i++) {
-               if (xy_sensors[i] < ATP_THRESHOLD)
+               if (xy_sensors[i] < threshold) {
+                       if (is_increasing)
+                               is_increasing = 0;
+
                        continue;
-               if ((i - 1 < 0) || (xy_sensors[i - 1] < ATP_THRESHOLD))
+               }
+
+               /*
+                * Makes the finger detection more versatile.  For example,
+                * two fingers with no gap will be detected.  Also, my
+                * tests show it less likely to have intermittent loss
+                * of multiple finger readings while moving around (scrolling).
+                *
+                * Changes the multiple finger detection to counting humps on
+                * sensors (transitions from nonincreasing to increasing)
+                * instead of counting transitions from low sensors (no
+                * finger reading) to high sensors (finger above
+                * sensor)
+                *
+                * - Jason Parekh <jasonparekh@gmail.com>
+                */
+               if (i < 1 || (!is_increasing && xy_sensors[i - 1] < xy_sensors[i])) {
                        (*fingers)++;
-               pcum += xy_sensors[i] * i;
-               psum += xy_sensors[i];
+                       is_increasing = 1;
+               } else if (i > 0 && xy_sensors[i - 1] >= xy_sensors[i]) {
+                       is_increasing = 0;
+               }
+
+               /*
+                * Subtracts threshold so a high sensor that just passes the threshold
+                * won't skew the calculated absolute coordinate.  Fixes an issue
+                * where slowly moving the mouse would occassionaly jump a number of
+                * pixels (let me restate--slowly moving the mouse makes this issue
+                * most apparent).
+                */
+               pcum += (xy_sensors[i] - threshold) * i;
+               psum += (xy_sensors[i] - threshold);
        }
 
        if (psum > 0) {