Move the cursor position rightward after rendering the character,
not before. This avoids complications that arise when the recursive
console_putc call has to wrap the line and/or scroll the display.
This also fixes the linewrap bug that crops off the rightmost column.

When the cursor is at the bottom of the display, a linefeed will not
move the cursor position further downward. Instead, the display scrolls
upward. Avoid the repeated add/subtract sequence by way of a single
subtraction at the initialization of console_struct_num_rows.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
 arch/m68k/kernel/head.S | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
index 852255cf60de..d0d77b1adbde 100644
--- a/arch/m68k/kernel/head.S
+++ b/arch/m68k/kernel/head.S
@@ -3400,6 +3400,7 @@ L(console_clear_loop):
 
 	movel	%d4,%d1				/* screen height in pixels */
 	divul	%a0@(FONT_DESC_HEIGHT),%d1	/* d1 = max num rows */
+	subil	#1,%d1				/* row range is 0 to num - 1 */
 
 	movel	%d0,%a2@(Lconsole_struct_num_columns)
 	movel	%d1,%a2@(Lconsole_struct_num_rows)
@@ -3546,15 +3547,14 @@ func_start	console_putc,%a0/%a1/%d0-%d7
 	cmpib	#10,%d7
 	jne	L(console_not_lf)
 	movel	%a0@(Lconsole_struct_cur_row),%d0
-	addil	#1,%d0
-	movel	%d0,%a0@(Lconsole_struct_cur_row)
 	movel	%a0@(Lconsole_struct_num_rows),%d1
 	cmpl	%d1,%d0
 	jcs	1f
-	subil	#1,%d0
-	movel	%d0,%a0@(Lconsole_struct_cur_row)
 	console_scroll
+	jra	L(console_exit)
 1:
+	addil	#1,%d0
+	movel	%d0,%a0@(Lconsole_struct_cur_row)
 	jra	L(console_exit)
 
 L(console_not_lf):
@@ -3581,12 +3581,6 @@ L(console_not_cr):
  */
 L(console_not_home):
 	movel	%a0@(Lconsole_struct_cur_column),%d0
-	addql	#1,%a0@(Lconsole_struct_cur_column)
-	movel	%a0@(Lconsole_struct_num_columns),%d1
-	cmpl	%d1,%d0
-	jcs	1f
-	console_putc	#'\n'	/* recursion is OK! */
-1:
 	movel	%a0@(Lconsole_struct_cur_row),%d1
 
 	/*
@@ -3633,6 +3627,23 @@ L(console_do_font_scanline):
 	addq	#1,%d1
 	dbra	%d7,L(console_read_char_scanline)
 
+	/*
+	 *	Register usage in the code below:
+	 *	a0 = pointer to console globals
+	 *	d0 = cursor column
+	 *	d1 = cursor column limit
+	 */
+
+	lea	%pc@(L(console_globals)),%a0
+
+	movel	%a0@(Lconsole_struct_cur_column),%d0
+	addil	#1,%d0
+	movel	%d0,%a0@(Lconsole_struct_cur_column)	/* Update cursor pos */
+	movel	%a0@(Lconsole_struct_num_columns),%d1
+	cmpl	%d1,%d0
+	jcs	L(console_exit)
+	console_putc	#'\n'		/* Line wrap using tail recursion */
+
 L(console_exit):
 func_return	console_putc
 
-- 
2.45.3

On Mär 19 2025, Finn Thain wrote:

> diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
> index 852255cf60de..d0d77b1adbde 100644
> --- a/arch/m68k/kernel/head.S
> +++ b/arch/m68k/kernel/head.S
> @@ -3400,6 +3400,7 @@ L(console_clear_loop):
>  
>  	movel	%d4,%d1				/* screen height in pixels */
>  	divul	%a0@(FONT_DESC_HEIGHT),%d1	/* d1 = max num rows */
> +	subil	#1,%d1				/* row range is 0 to num - 1 */

s/subil/subql/

> @@ -3546,15 +3547,14 @@ func_start	console_putc,%a0/%a1/%d0-%d7
>  	cmpib	#10,%d7
>  	jne	L(console_not_lf)
>  	movel	%a0@(Lconsole_struct_cur_row),%d0
> -	addil	#1,%d0
> -	movel	%d0,%a0@(Lconsole_struct_cur_row)
>  	movel	%a0@(Lconsole_struct_num_rows),%d1
>  	cmpl	%d1,%d0
>  	jcs	1f
> -	subil	#1,%d0
> -	movel	%d0,%a0@(Lconsole_struct_cur_row)
>  	console_scroll
> +	jra	L(console_exit)
>  1:
> +	addil	#1,%d0

s/addil/addql/

> @@ -3581,12 +3581,6 @@ L(console_not_cr):
>   */
>  L(console_not_home):
>  	movel	%a0@(Lconsole_struct_cur_column),%d0
> -	addql	#1,%a0@(Lconsole_struct_cur_column)
> -	movel	%a0@(Lconsole_struct_num_columns),%d1
> -	cmpl	%d1,%d0
> -	jcs	1f
> -	console_putc	#'\n'	/* recursion is OK! */
> -1:
>  	movel	%a0@(Lconsole_struct_cur_row),%d1
>  
>  	/*
> @@ -3633,6 +3627,23 @@ L(console_do_font_scanline):
>  	addq	#1,%d1
>  	dbra	%d7,L(console_read_char_scanline)
>  
> +	/*
> +	 *	Register usage in the code below:
> +	 *	a0 = pointer to console globals
> +	 *	d0 = cursor column
> +	 *	d1 = cursor column limit
> +	 */
> +
> +	lea	%pc@(L(console_globals)),%a0
> +
> +	movel	%a0@(Lconsole_struct_cur_column),%d0
> +	addil	#1,%d0

s/addil/addql/

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

On Wed, 19 Mar 2025, Andreas Schwab wrote:

> 
> s/subil/subql/
> 

> 
> s/addil/addql/
> 

Will do. Thanks.