earlyprintk,vga,kdb: Fix \b and \r for earlyprintk=vga with kdb

Allow kdb to work properly with with earlyprintk=vga by interpreting
the backspace and carriage return output characters.  These
interpretation of these characters is used for simple line editing
provided in the kdb shell.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: x86@kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index b9c830c12b4a..fa99bae75ace 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -41,6 +41,14 @@ static void early_vga_write(struct console *con, const char *str, unsigned n)
                                 writew(0x720, VGABASE + 2*(max_xpos*j + i));
                         current_ypos = max_ypos-1;
                 }
+#ifdef CONFIG_KGDB_KDB
+                if (c == '\b') {
+                        if (current_xpos > 0)
+                                current_xpos--;
+                } else if (c == '\r') {
+                        current_xpos = 0;
+                } else
+#endif
                 if (c == '\n') {
                         current_xpos = 0;
                         current_ypos++;