HID: Fix Speedlink VAD Cezanne support for some devices

Some devices of the "Speedlink VAD Cezanne" model need more aggressive fixing
than already done.

I made sure through testing that this patch would not interfere with the proper
working of a device that is bug-free. (The driver drops EV_REL events with
abs(val) >= 256, which are not achievable even on the highest laser resolution
hardware setting.)

Signed-off-by: Stefan Kriwanek <mail@stefankriwanek.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-speedlink.c

@@ -3,7 +3,7 @@
  *  Fixes "jumpy" cursor and removes nonexistent keyboard LEDS from
  *  the HID descriptor.
  *
- *  Copyright (c) 2011 Stefan Kriwanek <mail@stefankriwanek.de>
+ *  Copyright (c) 2011, 2013 Stefan Kriwanek <dev@stefankriwanek.de>
  */
 
 /*
@@ -46,8 +46,13 @@ static int speedlink_event(struct hid_device *hdev, struct hid_field *field,
 		struct hid_usage *usage, __s32 value)
 {
 	/* No other conditions due to usage_table. */
-	/* Fix "jumpy" cursor (invalid events sent by device). */
-	if (value == 256)
+
+	/* This fixes the "jumpy" cursor occuring due to invalid events sent
+	 * by the device. Some devices only send them with value==+256, others
+	 * don't. However, catching abs(value)>=256 is restrictive enough not
+	 * to interfere with devices that were bug-free (has been tested).
+	 */
+	if (abs(value) >= 256)
 		return 1;
 	/* Drop useless distance 0 events (on button clicks etc.) as well */
 	if (value == 0)