hid: egalax: Add event filtering

Use estimated signal-to-noise ratios to reduce noise and limit the
amount of events emitted.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: Stephane Chatty <chatty@enac.fr>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

drivers/hid/hid-egalax.c

@@ -25,6 +25,10 @@ MODULE_LICENSE("GPL");
 
 #include "hid-ids.h"
 
+/* estimated signal-to-noise ratios */
+#define SN_MOVE			4096
+#define SN_PRESSURE		32
+
 struct egalax_data {
 	__u16 x, y, z;
 	__u8 id;
@@ -57,17 +61,17 @@ static int egalax_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 			field->logical_maximum = 32760;
 			hid_map_usage(hi, usage, bit, max,
 					EV_ABS, ABS_MT_POSITION_X);
-			set_abs(input, ABS_MT_POSITION_X, field, 0);
+			set_abs(input, ABS_MT_POSITION_X, field, SN_MOVE);
 			/* touchscreen emulation */
-			set_abs(input, ABS_X, field, 0);
+			set_abs(input, ABS_X, field, SN_MOVE);
 			return 1;
 		case HID_GD_Y:
 			field->logical_maximum = 32760;
 			hid_map_usage(hi, usage, bit, max,
 					EV_ABS, ABS_MT_POSITION_Y);
-			set_abs(input, ABS_MT_POSITION_Y, field, 0);
+			set_abs(input, ABS_MT_POSITION_Y, field, SN_MOVE);
 			/* touchscreen emulation */
-			set_abs(input, ABS_Y, field, 0);
+			set_abs(input, ABS_Y, field, SN_MOVE);
 			return 1;
 		}
 		return 0;
@@ -93,9 +97,9 @@ static int egalax_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 			field->logical_minimum = 0;
 			hid_map_usage(hi, usage, bit, max,
 					EV_ABS, ABS_MT_PRESSURE);
-			set_abs(input, ABS_MT_PRESSURE, field, 0);
+			set_abs(input, ABS_MT_PRESSURE, field, SN_PRESSURE);
 			/* touchscreen emulation */
-			set_abs(input, ABS_PRESSURE, field, 0);
+			set_abs(input, ABS_PRESSURE, field, SN_PRESSURE);
 			return 1;
 		}
 		return 0;