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Subject[PATCH 5.10 45/48] Input: spaceball - fix parsing of movement data packets
Date
From: Leo L. Schwab <ewhac@ewhac.org>

commit bc7ec91718c49d938849697cfad98fcd9877cc26 upstream.

The spaceball.c module was not properly parsing the movement reports
coming from the device. The code read axis data as signed 16-bit
little-endian values starting at offset 2.

In fact, axis data in Spaceball movement reports are signed 16-bit
big-endian values starting at offset 3. This was determined first by
visually inspecting the data packets, and later verified by consulting:
http://spacemice.org/pdf/SpaceBall_2003-3003_Protocol.pdf

If this ever worked properly, it was in the time before Git...

Signed-off-by: Leo L. Schwab <ewhac@ewhac.org>
Link: https://lore.kernel.org/r/20211221101630.1146385-1-ewhac@ewhac.org
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/input/joystick/spaceball.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/input/joystick/spaceball.c
+++ b/drivers/input/joystick/spaceball.c
@@ -19,6 +19,7 @@
#include <linux/module.h>
#include <linux/input.h>
#include <linux/serio.h>
+#include <asm/unaligned.h>

#define DRIVER_DESC "SpaceTec SpaceBall 2003/3003/4000 FLX driver"

@@ -75,9 +76,15 @@ static void spaceball_process_packet(str

case 'D': /* Ball data */
if (spaceball->idx != 15) return;
- for (i = 0; i < 6; i++)
+ /*
+ * Skip first three bytes; read six axes worth of data.
+ * Axis values are signed 16-bit big-endian.
+ */
+ data += 3;
+ for (i = 0; i < ARRAY_SIZE(spaceball_axes); i++) {
input_report_abs(dev, spaceball_axes[i],
- (__s16)((data[2 * i + 3] << 8) | data[2 * i + 2]));
+ (__s16)get_unaligned_be16(&data[i * 2]));
+ }
break;

case 'K': /* Button data */

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