HID: Fix Speedlink VAD Cezanne support for some devices

commit 06bb5219118fb098f4b0c7dcb484b28a52bf1c14 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/drivers/hid/hid-speedlink.c b/drivers/hid/hid-speedlink.c
index a2f587d004e1..7112f3e832ee 100644
--- a/drivers/hid/hid-speedlink.c
+++ b/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)