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[PATCH] Input: synaptics - reject out of range position values

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The synaptics touchpad on the Acer Aspire One D250 will report y
coordinate values in excess of 8000 near the bottom of the touchpad,
well outside of the range of values that the synaptics documentation
says should be reported.

In addition, the y values abruptly change from very low values to these
very high values. After the calculation to invert the y coordinates,
userspace gets y coordinates that can jump suddenly between large
positive and moderately large negative values, causing sudden jumps in
the pointer position.

To work around this odd behavior, reject any coordinates with values
outside of absolute limits specified by Synaptics, which is 6143 for
both axes.

BugLink: http://bugs.launchpad.net/bugs/1001251
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
---
I'm not sure whether the limits here should be the hard-coded value or
the coordinates reported by the device when that's supported (i.e.
whether the coordinates reported by the device are always within the
range of 0 to 6143). If the latter is more appropriate I can modify the
patch to use the device-reported values and fall back to the hard-coded
values.

 drivers/input/mouse/synaptics.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
index e07eb9b..f62299d 100644
--- a/drivers/input/mouse/synaptics.c
+++ b/drivers/input/mouse/synaptics.c
@@ -40,6 +40,8 @@
  * Note that newer firmware allows querying device for maximum useable
  * coordinates.
  */
+#define XMAX 6143
+#define YMAX 6143
 #define XMIN_NOMINAL 1472
 #define XMAX_NOMINAL 5472
 #define YMIN_NOMINAL 1408
@@ -555,6 +557,9 @@ static int synaptics_parse_hw_state(const unsigned char buf[],
 		hw->right = (buf[0] & 0x02) ? 1 : 0;
 	}
 
+	if (hw->x > XMAX || hw->y > YMAX)
+		return 1;
+
 	return 0;
 }
 
-- 
1.7.9.5

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