[PATCH v3 1/5] m68k: Fix atari mouse movement

[PATCH v3 1/5] m68k: Fix atari mouse movement

[Michael Schmitz]

From: Miro Kropacek <miro.kropacek@gmail.com>

Kernels are built with -funsigned-char since version 6.2, resulting
in signed mouse position deltas getting misinterpreted as unsigned.

Cast deltas passed in (unsigned) scancode buffer to correctly
interpret sign.

Fixes: 3bc753c06dd02a35 ("kbuild: treat char as always unsigned")
Link: https://lists.debian.org/debian-68k/2026/08/msg00000.html
Signed-off-by: Miro Kropacek <miro.kropacek@gmail.com>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Cc: linux-input <linux-input@vger.kernel.org>

---

Changes in v2:

- change atamouse_interrupt function signature to signed char *,
  drop signed casts (Geert)
---
 arch/m68k/atari/atakeyb.c        | 2 +-
 arch/m68k/include/asm/atarikb.h  | 2 +-
 drivers/input/mouse/atarimouse.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/m68k/atari/atakeyb.c b/arch/m68k/atari/atakeyb.c
index 49a9a459bdf4..86ab73a79177 100644
--- a/arch/m68k/atari/atakeyb.c
+++ b/arch/m68k/atari/atakeyb.c
@@ -39,7 +39,7 @@ void (*atari_MIDI_interrupt_hook) (void);
 /* Hook for keyboard inputdev  driver */
 void (*atari_input_keyboard_interrupt_hook) (unsigned char, char);
 /* Hook for mouse inputdev  driver */
-void (*atari_input_mouse_interrupt_hook) (char *);
+void (*atari_input_mouse_interrupt_hook)(signed char *buf);
 EXPORT_SYMBOL(atari_input_keyboard_interrupt_hook);
 EXPORT_SYMBOL(atari_input_mouse_interrupt_hook);
 
diff --git a/arch/m68k/include/asm/atarikb.h b/arch/m68k/include/asm/atarikb.h
index 68f3622bf591..c5a84c7ee85d 100644
--- a/arch/m68k/include/asm/atarikb.h
+++ b/arch/m68k/include/asm/atarikb.h
@@ -37,7 +37,7 @@ extern void (*atari_MIDI_interrupt_hook) (void);
 /* Hook for keyboard inputdev  driver */
 extern void (*atari_input_keyboard_interrupt_hook) (unsigned char, char);
 /* Hook for mouse inputdev  driver */
-extern void (*atari_input_mouse_interrupt_hook) (char *);
+extern void (*atari_input_mouse_interrupt_hook)(signed char *buf);
 
 int atari_keyb_init(void);
 
diff --git a/drivers/input/mouse/atarimouse.c b/drivers/input/mouse/atarimouse.c
index b1219cc4d9a2..6bac2288c494 100644
--- a/drivers/input/mouse/atarimouse.c
+++ b/drivers/input/mouse/atarimouse.c
@@ -60,7 +60,7 @@ extern int atari_mouse_buttons;
 
 static struct input_dev *atamouse_dev;
 
-static void atamouse_interrupt(char *buf)
+static void atamouse_interrupt(signed char *buf)
 {
 	int buttons, dx, dy;
 
-- 
2.17.1

[PATCH v4] m68k: Fix atari mouse movement

[Miro Kropacek]

Kernels are built with -funsigned-char since version 6.2, resulting in
the signed 8-bit position deltas reported by the IKBD being
misinterpreted as unsigned.

Carry the sign in the type of the mouse interrupt hook. The scancode
buffer is shared with the keyboard and joystick paths, where unsigned is
correct, so it stays unsigned and is cast at the single call site that
passes it to the mouse driver.

Fixes: 3bc753c06dd02a35 ("kbuild: treat char as always unsigned")
Link: https://lists.debian.org/debian-68k/2026/08/msg00000.html
Signed-off-by: Miro Kropacek <miro.kropacek@gmail.com>
Reviewed-by: Michael Schmitz <schmitzmic@gmail.com>
Cc: linux-input <linux-input@vger.kernel.org>
---

Changes in v4:

- cast at the atakeyb.c call site, so the signed hook no longer
  produces a -Wpointer-sign warning there

The functional change was tested on an Atari Falcon030 with CT60 in its
v3 form; v4 only adds the cast at the call site.

Note that the original version of this patch, which cast the two deltas
inside atamouse_interrupt() and left the hook as char *, produced no
warning at all. The signature change was your suggestion, Geert - if you
prefer the earlier form, say so and I will send that instead.

 arch/m68k/atari/atakeyb.c        | 5 +++--
 arch/m68k/include/asm/atarikb.h  | 2 +-
 drivers/input/mouse/atarimouse.c | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/m68k/atari/atakeyb.c b/arch/m68k/atari/atakeyb.c
index 49a9a459bdf4..1eadeb8e4d7b 100644
--- a/arch/m68k/atari/atakeyb.c
+++ b/arch/m68k/atari/atakeyb.c
@@ -39,7 +39,7 @@ void (*atari_MIDI_interrupt_hook) (void);
 /* Hook for keyboard inputdev  driver */
 void (*atari_input_keyboard_interrupt_hook) (unsigned char, char);
 /* Hook for mouse inputdev  driver */
-void (*atari_input_mouse_interrupt_hook) (char *);
+void (*atari_input_mouse_interrupt_hook)(signed char *buf);
 EXPORT_SYMBOL(atari_input_keyboard_interrupt_hook);
 EXPORT_SYMBOL(atari_input_mouse_interrupt_hook);
 
@@ -260,7 +260,8 @@ static irqreturn_t atari_keyboard_interrupt(int irq, void *dummy)
 			if (kb_state.len == 3) {
 				kb_state.state = KEYBOARD;
 				if (atari_input_mouse_interrupt_hook)
-					atari_input_mouse_interrupt_hook(kb_state.buf);
+					atari_input_mouse_interrupt_hook(
+						(signed char *)kb_state.buf);
 			}
 			break;
 
diff --git a/arch/m68k/include/asm/atarikb.h b/arch/m68k/include/asm/atarikb.h
index 68f3622bf591..c5a84c7ee85d 100644
--- a/arch/m68k/include/asm/atarikb.h
+++ b/arch/m68k/include/asm/atarikb.h
@@ -37,7 +37,7 @@ extern void (*atari_MIDI_interrupt_hook) (void);
 /* Hook for keyboard inputdev  driver */
 extern void (*atari_input_keyboard_interrupt_hook) (unsigned char, char);
 /* Hook for mouse inputdev  driver */
-extern void (*atari_input_mouse_interrupt_hook) (char *);
+extern void (*atari_input_mouse_interrupt_hook)(signed char *buf);
 
 int atari_keyb_init(void);
 
diff --git a/drivers/input/mouse/atarimouse.c b/drivers/input/mouse/atarimouse.c
index b1219cc4d9a2..6bac2288c494 100644
--- a/drivers/input/mouse/atarimouse.c
+++ b/drivers/input/mouse/atarimouse.c
@@ -60,7 +60,7 @@ extern int atari_mouse_buttons;
 
 static struct input_dev *atamouse_dev;
 
-static void atamouse_interrupt(char *buf)
+static void atamouse_interrupt(signed char *buf)
 {
 	int buttons, dx, dy;
 
-- 
2.43.0

Re: [PATCH v4] m68k: Fix atari mouse movement

[Dmitry Torokhov]

Hi Miro,

On Wed, Oct 21, 2026 at 10:03:37AM +1000, Miro Kropacek wrote:
> Kernels are built with -funsigned-char since version 6.2, resulting in
> the signed 8-bit position deltas reported by the IKBD being
> misinterpreted as unsigned.
> 
> Carry the sign in the type of the mouse interrupt hook. The scancode
> buffer is shared with the keyboard and joystick paths, where unsigned is
> correct, so it stays unsigned and is cast at the single call site that
> passes it to the mouse driver.

The hook receives the byte stream, so I would rather have it accept u8*
and then do signed cast for displacement values (and only them).

Thanks.

-- 
Dmitry