[PATCH v4] m68k: Fix atari mouse movement

[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

[PATCH v5] 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.

The hook is handed a raw IKBD packet, so take it as a byte stream and
apply the sign to the two displacement values alone.

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

Changes in v5:

- take the packet as u8 * and cast only the two displacement values,
  as suggested; this drops the call-site cast v4 needed, and with it
  the -Wpointer-sign warning
- add the types include atarikb.h now relies on

The same cast of the two displacement values was tested on an Atari
Falcon030 with CT60 in v1 of this patch; v5 differs from it only in the
type of the hook argument.

Michael's Reviewed-by from v3 is dropped, as the approach has changed
twice since.

 arch/m68k/atari/atakeyb.c        | 2 +-
 arch/m68k/include/asm/atarikb.h  | 4 +++-
 drivers/input/mouse/atarimouse.c | 6 +++---
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/m68k/atari/atakeyb.c b/arch/m68k/atari/atakeyb.c
index 49a9a459bdf4..b715e2b8351c 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)(u8 *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..bdf67bff1472 100644
--- a/arch/m68k/include/asm/atarikb.h
+++ b/arch/m68k/include/asm/atarikb.h
@@ -15,6 +15,8 @@
 #ifndef _LINUX_ATARIKB_H
 #define _LINUX_ATARIKB_H
 
+#include <linux/types.h>
+
 void ikbd_write(const char *, int);
 void ikbd_mouse_button_action(int mode);
 void ikbd_mouse_rel_pos(void);
@@ -37,7 +39,7 @@ 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)(u8 *buf);
 
 int atari_keyb_init(void);
 
diff --git a/drivers/input/mouse/atarimouse.c b/drivers/input/mouse/atarimouse.c
index b1219cc4d9a2..c5b794262e85 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(u8 *buf)
 {
 	int buttons, dx, dy;
 
@@ -71,8 +71,8 @@ static void atamouse_interrupt(char *buf)
 #endif
 
 	/* only relative events get here */
-	dx = buf[1];
-	dy = buf[2];
+	dx = (s8)buf[1];
+	dy = (s8)buf[2];
 
 	input_report_rel(atamouse_dev, REL_X, dx);
 	input_report_rel(atamouse_dev, REL_Y, dy);
-- 
2.43.0

Re: [PATCH v5] m68k: Fix atari mouse movement

[Michael Schmitz]

Hi Miro,

Am 21.10.2026 um 15:23 schrieb 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.
>
> The hook is handed a raw IKBD packet, so take it as a byte stream and
> apply the sign to the two displacement values alone.
>
> Fixes: 3bc753c06dd02a35 ("kbuild: treat char as always unsigned")
> Link: https://lists.debian.org/debian-68k/2026/08/msg00000.html
> Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Signed-off-by: Miro Kropacek <miro.kropacek@gmail.com>
> Cc: linux-input <linux-input@vger.kernel.org>
> ---
>
> Changes in v5:
>
> - take the packet as u8 * and cast only the two displacement values,
>   as suggested; this drops the call-site cast v4 needed, and with it
>   the -Wpointer-sign warning
> - add the types include atarikb.h now relies on
>
> The same cast of the two displacement values was tested on an Atari
> Falcon030 with CT60 in v1 of this patch; v5 differs from it only in the
> type of the hook argument.
>
> Michael's Reviewed-by from v3 is dropped, as the approach has changed
> twice since.

Dmitry's reasoning makes sense to me, so we're back on v1 with no change 
in functionality.

Looks good to me, feel free to add my Reviewed-by if it helps get this 
merged.

Cheers,

	Michael


>
>  arch/m68k/atari/atakeyb.c        | 2 +-
>  arch/m68k/include/asm/atarikb.h  | 4 +++-
>  drivers/input/mouse/atarimouse.c | 6 +++---
>  3 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/m68k/atari/atakeyb.c b/arch/m68k/atari/atakeyb.c
> index 49a9a459bdf4..b715e2b8351c 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)(u8 *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..bdf67bff1472 100644
> --- a/arch/m68k/include/asm/atarikb.h
> +++ b/arch/m68k/include/asm/atarikb.h
> @@ -15,6 +15,8 @@
>  #ifndef _LINUX_ATARIKB_H
>  #define _LINUX_ATARIKB_H
>
> +#include <linux/types.h>
> +
>  void ikbd_write(const char *, int);
>  void ikbd_mouse_button_action(int mode);
>  void ikbd_mouse_rel_pos(void);
> @@ -37,7 +39,7 @@ 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)(u8 *buf);
>
>  int atari_keyb_init(void);
>
> diff --git a/drivers/input/mouse/atarimouse.c b/drivers/input/mouse/atarimouse.c
> index b1219cc4d9a2..c5b794262e85 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(u8 *buf)
>  {
>  	int buttons, dx, dy;
>
> @@ -71,8 +71,8 @@ static void atamouse_interrupt(char *buf)
>  #endif
>
>  	/* only relative events get here */
> -	dx = buf[1];
> -	dy = buf[2];
> +	dx = (s8)buf[1];
> +	dy = (s8)buf[2];
>
>  	input_report_rel(atamouse_dev, REL_X, dx);
>  	input_report_rel(atamouse_dev, REL_Y, dy);
>

Re: [PATCH v5] m68k: Fix atari mouse movement

[Geert Uytterhoeven]

On Wed, 21 Oct 2026 at 04:51, Michael Schmitz <schmitzmic@gmail.com> wrote:
> Am 21.10.2026 um 15:23 schrieb 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.
> >
> > The hook is handed a raw IKBD packet, so take it as a byte stream and
> > apply the sign to the two displacement values alone.
> >
> > Fixes: 3bc753c06dd02a35 ("kbuild: treat char as always unsigned")
> > Link: https://lists.debian.org/debian-68k/2026/08/msg00000.html
> > Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> > Signed-off-by: Miro Kropacek <miro.kropacek@gmail.com>
> > Cc: linux-input <linux-input@vger.kernel.org>
> > ---
> >
> > Changes in v5:
> >
> > - take the packet as u8 * and cast only the two displacement values,
> >   as suggested; this drops the call-site cast v4 needed, and with it
> >   the -Wpointer-sign warning
> > - add the types include atarikb.h now relies on
> >
> > The same cast of the two displacement values was tested on an Atari
> > Falcon030 with CT60 in v1 of this patch; v5 differs from it only in the
> > type of the hook argument.
> >
> > Michael's Reviewed-by from v3 is dropped, as the approach has changed
> > twice since.
>
> Dmitry's reasoning makes sense to me, so we're back on v1 with no change
> in functionality.

If it's just a byte stream, one might not bother doing s/char/u8/, as both
are the same type anyway... and then we're really back at v1.

> Looks good to me, feel free to add my Reviewed-by if it helps get this
> merged.

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
for the arch/m68k files:
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds