m68k: Don't unregister boot console needlessly

When MACH_IS_MVME147, the boot console calls mvme147_scc_write() to
generate console output. That will continue to work even after
debug_cons_nputs() becomes unavailable so there's no need to
unregister the boot console.

Take the opportunity to remove a repeated MACH_IS_* test. Use the
actual .write method (instead of a wrapper) and test that pointer
instead. This means adding an unused parameter to debug_cons_nputs() for
consistency with the struct console API.

early_printk.c is only built when CONFIG_EARLY_PRINTK=y. As of late,
head.S is only built when CONFIG_MMU_MOTOROLA=y. So let the former symbol
depend on the latter, to obviate some ifdef conditionals.

Cc: Daniel Palmer <daniel@0x0f.com>
Fixes: 077b33b ("m68k: mvme147: Reinstate early console")
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/d1d4328e5aa9a87bd8352529ce62b767731c0530.1743467205.git.fthain@linux-m68k.org
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Author: fthain

arch/m68k/Kconfig.debug

@@ -10,7 +10,7 @@ config BOOTPARAM_STRING
 
 config EARLY_PRINTK
 	bool "Early printk"
-	depends on !(SUN3 || M68000 || COLDFIRE)
+	depends on MMU_MOTOROLA
 	help
 	  Write kernel log output directly to a serial port.
 	  Where implemented, output goes to the framebuffer as well.

arch/m68k/kernel/early_printk.c

@@ -16,25 +16,10 @@
 #include "../mvme147/mvme147.h"
 #include "../mvme16x/mvme16x.h"
 
-asmlinkage void __init debug_cons_nputs(const char *s, unsigned n);
-
-static void __ref debug_cons_write(struct console *c,
-				   const char *s, unsigned n)
-{
-#if !(defined(CONFIG_SUN3) || defined(CONFIG_M68000) || \
-      defined(CONFIG_COLDFIRE))
-	if (MACH_IS_MVME147)
-		mvme147_scc_write(c, s, n);
-	else if (MACH_IS_MVME16x)
-		mvme16x_cons_write(c, s, n);
-	else
-		debug_cons_nputs(s, n);
-#endif
-}
+asmlinkage void __init debug_cons_nputs(struct console *c, const char *s, unsigned int n);
 
 static struct console early_console_instance = {
 	.name  = "debug",
-	.write = debug_cons_write,
 	.flags = CON_PRINTBUFFER | CON_BOOT,
 	.index = -1
 };
@@ -44,27 +29,28 @@ static int __init setup_early_printk(char *buf)
 	if (early_console || buf)
 		return 0;
 
+	if (MACH_IS_MVME147)
+		early_console_instance.write = mvme147_scc_write;
+	else if (MACH_IS_MVME16x)
+		early_console_instance.write = mvme16x_cons_write;
+	else
+		early_console_instance.write = debug_cons_nputs;
 	early_console = &early_console_instance;
 	register_console(early_console);
 
 	return 0;
 }
 early_param("earlyprintk", setup_early_printk);
 
-/*
- * debug_cons_nputs() defined in arch/m68k/kernel/head.S cannot be called
- * after init sections are discarded (for platforms that use it).
- */
-#if !(defined(CONFIG_SUN3) || defined(CONFIG_M68000) || \
-      defined(CONFIG_COLDFIRE))
-
 static int __init unregister_early_console(void)
 {
-	if (!early_console || MACH_IS_MVME16x)
-		return 0;
+	/*
+	 * debug_cons_nputs() defined in arch/m68k/kernel/head.S cannot be
+	 * called after init sections are discarded (for platforms that use it).
+	 */
+	if (early_console && early_console->write == debug_cons_nputs)
+		return unregister_console(early_console);
 
-	return unregister_console(early_console);
+	return 0;
 }
 late_initcall(unregister_early_console);
-
-#endif

arch/m68k/kernel/head.S

@@ -3263,8 +3263,8 @@ func_return	putn
  *	turns around and calls the internal routines.  This routine
  *	is used by the boot console.
  *
- *	The calling parameters are:
- *		void debug_cons_nputs(const char *str, unsigned length)
+ *	The function signature is -
+ *		void debug_cons_nputs(struct console *c, const char *s, unsigned int n)
  *
  *	This routine does NOT understand variable arguments only
  *	simple strings!
@@ -3273,8 +3273,8 @@ ENTRY(debug_cons_nputs)
 	moveml	%d0/%d1/%a0,%sp@-
 	movew	%sr,%sp@-
 	ori	#0x0700,%sr
-	movel	%sp@(18),%a0		/* fetch parameter */
-	movel	%sp@(22),%d1		/* fetch parameter */
+	movel	%sp@(22),%a0		/* char *s */
+	movel	%sp@(26),%d1		/* unsigned int n */
 	jra	2f
 1:
 #ifdef CONSOLE_DEBUG