m68k: Fix lost column on framebuffer debug console

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>
Tested-by: Stan Johnson <userm57@yahoo.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/9d4e8c68a456d5f2bc254ac6f87a472d066ebd5e.1743115195.git.fthain@linux-m68k.org
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
index 852255cf60dec13214efeccc934b5fe571b60576..9bd8adaa756dbe06376c5ae6f12f92d8c12ab566 100644 (file)
--- 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 */
+       subql   #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:
+       addql   #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
+       addql   #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