Input: appletouch - fix integer overflow issue

When reading data from Geyser 2 touchpads used on post Oct 2005 Apple
PowerBooks the driver was casting X and Y coordinates values to
'signed char'. Testing on one of such PowerBooks I have noticed that
touchpad always generates positive values, but some of them are greater
that 127, and thus, when cast to 'signed char' being interpreted as
a negative.

Such bigger values have been observed infrequently, closer to the
edges of a touchpad, so the problem was not very visible.
Nevertheless, the patch would potentially improve touchpad
driver accuracy.

Signed-off-by: Vadim Zaliva <lord@crocodile.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/input/mouse/appletouch.c b/drivers/input/mouse/appletouch.c
index 908b5b44052f..53ec7ddd1826 100644
--- a/drivers/input/mouse/appletouch.c
+++ b/drivers/input/mouse/appletouch.c
@@ -205,8 +205,8 @@ struct atp {
         bool                    overflow_warned;
         int                     x_old;          /* last reported x/y, */
         int                     y_old;          /* used for smoothing */
-        signed char             xy_cur[ATP_XSENSORS + ATP_YSENSORS];
-        signed char             xy_old[ATP_XSENSORS + ATP_YSENSORS];
+        u8                      xy_cur[ATP_XSENSORS + ATP_YSENSORS];
+        u8                      xy_old[ATP_XSENSORS + ATP_YSENSORS];
         int                     xy_acc[ATP_XSENSORS + ATP_YSENSORS];
         int                     idlecount;      /* number of empty packets */
         struct work_struct      work;
@@ -531,7 +531,7 @@ static void atp_complete_geyser_1_2(struct urb *urb)
 
         for (i = 0; i < ATP_XSENSORS + ATP_YSENSORS; i++) {
                 /* accumulate the change */
-                signed char change = dev->xy_old[i] - dev->xy_cur[i];
+                int change = dev->xy_old[i] - dev->xy_cur[i];
                 dev->xy_acc[i] -= change;
 
                 /* prevent down drifting */