m68k: Multi-platform EARLY_PRINTK

Make the boot console available to more m68k platforms by leveraging
the head.S debug console.

The boot console is enabled by the "earlyprintk" command line argument
which is how most other architectures do this.

This is a change of behaviour for the Mac but does not negatively impact
the common use-case which is not debugging.

This is also a change of behaviour for other platforms because it means
the serial port stays quiet when CONFIG_EARLY_PRINTK is not enabled. This
is also an improvement for the common use-case.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stephen N Chivers <schivers@csc.com.au>
[Geert: CONSOLE_DEBUG should depend on CONFIG_FONT_SUPPORT]
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Documentation/kernel-parameters.txt

@@ -892,7 +892,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			(mmio) or 32-bit (mmio32).
 			The options are the same as for ttyS, above.
 
-	earlyprintk=	[X86,SH,BLACKFIN,ARM]
+	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k]
 			earlyprintk=vga
 			earlyprintk=efi
 			earlyprintk=xen

arch/m68k/Kconfig.debug

@@ -12,12 +12,17 @@ config BOOTPARAM_STRING
 
 config EARLY_PRINTK
 	bool "Early printk"
-	depends on MVME16x || MAC
+	depends on !(SUN3 || M68360 || M68000 || COLDFIRE)
 	help
           Write kernel log output directly to a serial port.
+          Where implemented, output goes to the framebuffer as well.
+          PROM console functionality on Sun 3x is not affected by this option.
+
+          Pass "earlyprintk" on the kernel command line to get a
+          boot console.
 
           This is useful for kernel debugging when your machine crashes very
-          early before the console code is initialized.
+          early, i.e. before the normal console driver is loaded.
           You should normally say N here, unless you want to debug such a crash.
 
 if !MMU

arch/m68k/kernel/Makefile

@@ -25,3 +25,5 @@ obj-$(CONFIG_HAS_DMA)	+= dma.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
 obj-$(CONFIG_BOOTINFO_PROC)	+= bootinfo_proc.o
 
+obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
+

arch/m68k/kernel/early_printk.c

@@ -0,0 +1,62 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (c) 2014 Finn Thain
+ */
+
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <asm/setup.h>
+
+asmlinkage void __init debug_cons_nputs(const char *s, unsigned n);
+
+static void debug_cons_write(struct console *c,
+			     const char *s, unsigned n)
+{
+	debug_cons_nputs(s, n);
+}
+
+static struct console early_console_instance = {
+	.name  = "debug",
+	.write = debug_cons_write,
+	.flags = CON_PRINTBUFFER | CON_BOOT,
+	.index = -1
+};
+
+static int __init setup_early_printk(char *buf)
+{
+	/* MVME16x registers an early console after interrupt setup. */
+	if (MACH_IS_MVME16x)
+		return 0;
+
+	if (early_console || buf)
+		return 0;
+
+	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_M68360) || \
+      defined(CONFIG_M68000) || defined(CONFIG_COLDFIRE))
+
+static int __init unregister_early_console(void)
+{
+	if (!early_console)
+		return 0;
+
+	return unregister_console(early_console);
+}
+late_initcall(unregister_early_console);
+
+#endif

arch/m68k/kernel/head.S

@@ -221,7 +221,7 @@
  * MMU_PRINT:	There is a routine built into head.S that can display the
  * MMU data structures.  It outputs its result through the serial_putc
  * interface.  So where ever that winds up driving data, that's where the
- * mmu struct will appear.  On the Macintosh that's typically the console.
+ * mmu struct will appear.
  *
  * SERIAL_DEBUG:	There are a series of putc() macro statements
  * scattered through out the code to give progress of status to the
@@ -249,8 +249,8 @@
  * USE_MFP:	Use the ST-MFP port (Modem1) for serial debug.
  *
  * Macintosh constants:
- * MAC_USE_SCC_A: Use SCC port A (modem) for serial debug and early console.
- * MAC_USE_SCC_B: Use SCC port B (printer) for serial debug and early console.
+ * MAC_USE_SCC_A: Use SCC port A (modem) for serial debug.
+ * MAC_USE_SCC_B: Use SCC port B (printer) for serial debug.
  */
 
 #include <linux/linkage.h>
@@ -267,27 +267,17 @@
 #include <asm/pgtable.h>
 #include <asm/page.h>
 #include <asm/asm-offsets.h>
-
 #ifdef CONFIG_MAC
-
-#include <asm/machw.h>
-
-#ifdef CONFIG_FRAMEBUFFER_CONSOLE
-#define CONSOLE_DEBUG
+#  include <asm/machw.h>
 #endif
 
 #ifdef CONFIG_EARLY_PRINTK
-#define SERIAL_DEBUG
-#else
-#undef SERIAL_DEBUG
+#  define SERIAL_DEBUG
+#  if defined(CONFIG_MAC) && defined(CONFIG_FONT_SUPPORT)
+#    define CONSOLE_DEBUG
+#  endif
 #endif
 
-#else /* !CONFIG_MAC */
-
-#define SERIAL_DEBUG
-
-#endif /* !CONFIG_MAC */
-
 #undef MMU_PRINT
 #undef MMU_NOCACHE_KERNEL
 #undef DEBUG
@@ -3213,21 +3203,19 @@ func_start	putn,%d0-%d2
 
 func_return	putn
 
-#ifdef CONFIG_MAC
+#ifdef CONFIG_EARLY_PRINTK
 /*
- *	mac_early_print
- *
  *	This routine takes its parameters on the stack.  It then
  *	turns around and calls the internal routines.  This routine
  *	is used by the boot console.
  *
  *	The calling parameters are:
- *		void mac_early_print(const char *str, unsigned length);
+ *		void debug_cons_nputs(const char *str, unsigned length)
  *
  *	This routine does NOT understand variable arguments only
  *	simple strings!
  */
-ENTRY(mac_early_print)
+ENTRY(debug_cons_nputs)
 	moveml	%d0/%d1/%a0,%sp@-
 	movew	%sr,%sp@-
 	ori	#0x0700,%sr
@@ -3249,7 +3237,7 @@ ENTRY(mac_early_print)
 	movew	%sp@+,%sr
 	moveml	%sp@+,%d0/%d1/%a0
 	rts
-#endif /* CONFIG_MAC */
+#endif /* CONFIG_EARLY_PRINTK */
 
 #if defined(CONFIG_HP300) || defined(CONFIG_APOLLO)
 func_start	set_leds,%d0/%a0

arch/m68k/mac/config.c

@@ -71,31 +71,6 @@ static void mac_get_model(char *str);
 static void mac_identify(void);
 static void mac_report_hardware(void);
 
-#ifdef CONFIG_EARLY_PRINTK
-asmlinkage void __init mac_early_print(const char *s, unsigned n);
-
-static void __init mac_early_cons_write(struct console *con,
-                                 const char *s, unsigned n)
-{
-	mac_early_print(s, n);
-}
-
-static struct console __initdata mac_early_cons = {
-	.name  = "early",
-	.write = mac_early_cons_write,
-	.flags = CON_PRINTBUFFER | CON_BOOT,
-	.index = -1
-};
-
-int __init mac_unregister_early_cons(void)
-{
-	/* mac_early_print can't be used after init sections are discarded */
-	return unregister_console(&mac_early_cons);
-}
-
-late_initcall(mac_unregister_early_cons);
-#endif
-
 static void __init mac_sched_init(irq_handler_t vector)
 {
 	via_init_clock(vector);
@@ -190,10 +165,6 @@ void __init config_mac(void)
 	mach_beep = mac_mksound;
 #endif
 
-#ifdef CONFIG_EARLY_PRINTK
-	register_console(&mac_early_cons);
-#endif
-
 	/*
 	 * Determine hardware present
 	 */