ARM: Add an earlyprintk debug console

This patch allows an earlyprintk console if CONFIG_DEBUG_LL is enabled,
using the printch asm function.

The patch is based on the original work by Sascha Hauer.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Pavel Machek <pavel@ucw.cz>

3 files changed, 66 insertions, 0 deletions

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 1a6f70e52921..feb7b11ed5b8 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -71,6 +71,14 @@ config DEBUG_LL
           in the kernel.  This is helpful if you are debugging code that
           executes before the console is initialized.
 
+config EARLY_PRINTK
+        bool "Early printk"
+        depends on DEBUG_LL
+        help
+          Say Y here if you want to have an early console using the
+          kernel low-level debugging functions. Add earlyprintk to your
+          kernel parameters to enable this console.
+
 config DEBUG_ICEDCC
         bool "Kernel low-level debugging via EmbeddedICE DCC channel"
         depends on DEBUG_LL
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 79087dd6d869..d0e40b7d5f42 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -52,5 +52,6 @@ endif
 
 head-y                  := head$(MMUEXT).o
 obj-$(CONFIG_DEBUG_LL)  += debug.o
+obj-$(CONFIG_EARLY_PRINTK)      += early_printk.o
 
 extra-y := $(head-y) init_task.o vmlinux.lds
diff --git a/arch/arm/kernel/early_printk.c b/arch/arm/kernel/early_printk.c
new file mode 100644
index 000000000000..85aa2b292692
--- /dev/null
+++ b/arch/arm/kernel/early_printk.c
@@ -0,0 +1,57 @@
+/*
+ *  linux/arch/arm/kernel/early_printk.c
+ *
+ *  Copyright (C) 2009 Sascha Hauer <s.hauer@pengutronix.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+
+extern void printch(int);
+
+static void early_write(const char *s, unsigned n)
+{
+        while (n-- > 0) {
+                if (*s == '\n')
+                        printch('\r');
+                printch(*s);
+                s++;
+        }
+}
+
+static void early_console_write(struct console *con, const char *s, unsigned n)
+{
+        early_write(s, n);
+}
+
+static struct console early_console = {
+        .name =         "earlycon",
+        .write =        early_console_write,
+        .flags =        CON_PRINTBUFFER | CON_BOOT,
+        .index =        -1,
+};
+
+asmlinkage void early_printk(const char *fmt, ...)
+{
+        char buf[512];
+        int n;
+        va_list ap;
+
+        va_start(ap, fmt);
+        n = vscnprintf(buf, sizeof(buf), fmt, ap);
+        early_write(buf, n);
+        va_end(ap);
+}
+
+static int __init setup_early_printk(char *buf)
+{
+        register_console(&early_console);
+        return 0;
+}
+
+early_param("earlyprintk", setup_early_printk);