diff mbox series

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

Message ID 20241028173914.68311-1-jason.gerecke@wacom.com
State New
Headers show
Series wacom: Interpret tilt data from Intuos Pro BT as signed values | expand

Commit Message

Gerecke, Jason Oct. 28, 2024, 5:39 p.m. UTC 
From: Jason Gerecke <jason.gerecke@wacom.com>

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: stable@vger.kernel.org # 4.11+
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
---
 drivers/hid/wacom_wac.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Jiri Kosina Nov. 6, 2024, 2:57 p.m. UTC | #1 
On Mon, 28 Oct 2024, Gerecke, Jason wrote:

> From: Jason Gerecke <jason.gerecke@wacom.com>
> 
> 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: stable@vger.kernel.org # 4.11+
> Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>

I have added 'HID: ' prefix to the subject line and applied, thanks.
diff mbox series

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]));