wacom: Interpret tilt data from Intuos Pro BT as signed values

Commit Message

Gerecke, Jason Oct. 28, 2024, 5:39 p.m. UTC

From: Jason Gerecke <[e-mail]>

The tilt data contained in the Bluetooth packets of an Intuos Pro are
supposed to be interpreted as signed values. Simply casting the values
to type `char` is not guaranteed to work since it is implementation-
defined whether it is signed or unsigned. At least one user has noticed
the data being reported incorrectly on their system. To ensure that the
data is interpreted properly, we specifically cast to `signed char`
instead.

Link: https://github.com/linuxwacom/input-wacom/issues/445
Fixes: 4922cd26f03c ("HID: wacom: Support 2nd-gen Intuos Pro's Bluetooth classic interface")
CC: [e-mail] # 4.11+
Signed-off-by: Jason Gerecke <[e-mail]>
---
 drivers/hid/wacom_wac.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Patch

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 413606bdf476..5a599c90e7a2 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -1353,9 +1353,9 @@  static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
 					rotation -= 1800;
 
 				input_report_abs(pen_input, ABS_TILT_X,
-						 (char)frame[7]);
+						 (signed char)frame[7]);
 				input_report_abs(pen_input, ABS_TILT_Y,
-						 (char)frame[8]);
+						 (signed char)frame[8]);
 				input_report_abs(pen_input, ABS_Z, rotation);
 				input_report_abs(pen_input, ABS_WHEEL,
 						 get_unaligned_le16(&frame[11]));