xen: use the hvc console infrastructure for Xen console

Implement a Xen back-end for hvc console.

* * *
Add early printk support via hvc console, enable using
"earlyprintk=xen" on the kernel command line.

From: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Olof Johansson <olof@lixom.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/early_printk.c b/arch/x86_64/kernel/early_printk.c
index 296d2b0c5d88..fd9aff3f3890 100644
--- a/arch/x86_64/kernel/early_printk.c
+++ b/arch/x86_64/kernel/early_printk.c
@@ -6,6 +6,7 @@
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/fcntl.h>
+#include <xen/hvc-console.h>
 
 /* Simple VGA output */
 
@@ -242,6 +243,10 @@ static int __init setup_early_printk(char *buf)
                 simnow_init(buf + 6);
                 early_console = &simnow_console;
                 keep_early = 1;
+#ifdef CONFIG_HVC_XEN
+        } else if (!strncmp(buf, "xen", 3)) {
+                early_console = &xenboot_console;
+#endif
         }
 
         if (keep_early)