linux-kernel - [PATCH 3.2 136/149] HID: Fix Speedlink VAD Cezanne support for some devices

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Message-ID: <lsq.1382345188.252123479@decadent.org.uk>
Date:	Mon, 21 Oct 2013 09:46:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Stefan Kriwanek" <mail@...fankriwanek.de>,
	"Jiri Kosina" <jkosina@...e.cz>,
	"Stefan Kriwanek" <dev@...fankriwanek.de>
Subject: [PATCH 3.2 136/149] HID: Fix Speedlink VAD Cezanne support for
 some devices

3.2.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Kriwanek <dev@...fankriwanek.de>

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@...fankriwanek.de>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/hid/hid-speedlink.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- 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@...fankriwanek.de>
+ *  Copyright (c) 2011, 2013 Stefan Kriwanek <dev@...fankriwanek.de>
  */
 
 /*
@@ -48,8 +48,13 @@ static int speedlink_event(struct hid_de
 		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)

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