[PATCH 1/2] hvc_xen: add earlycon support

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Introduce EARLYCON support in hvc_xen, useful for early debugging on arm
and arm64, where xen early_printk is not available. Differently from
xenboot_write_console on x86, we won't just return if !xen_pv_domain(),
because arm and arm64 guests are actually xen_hvm_domain() from linux
pov, and also because we want to capture all possible writes, including
the ones earlier than xen_early_init().

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 drivers/tty/hvc/hvc_xen.c |   48 ++++++++++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index fa816b7..34e8e9f 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -25,6 +25,7 @@
 #include <linux/init.h>
 #include <linux/types.h>
 #include <linux/list.h>
+#include <linux/serial_core.h>
 
 #include <asm/io.h>
 #include <asm/xen/hypervisor.h>
@@ -597,21 +598,11 @@ static int xen_cons_init(void)
 }
 console_initcall(xen_cons_init);
 
-#ifdef CONFIG_EARLY_PRINTK
-static void xenboot_write_console(struct console *console, const char *string,
-				  unsigned len)
+static void domU_write_early_console(const char *string, unsigned len)
 {
 	unsigned int linelen, off = 0;
 	const char *pos;
 
-	if (!xen_pv_domain())
-		return;
-
-	dom0_write_console(0, string, len);
-
-	if (xen_initial_domain())
-		return;
-
 	domU_write_console(0, "(early) ", 8);
 	while (off < len && NULL != (pos = strchr(string+off, '\n'))) {
 		linelen = pos-string+off;
@@ -625,6 +616,21 @@ static void xenboot_write_console(struct console *console, const char *string,
 		domU_write_console(0, string+off, len-off);
 }
 
+#ifdef CONFIG_EARLY_PRINTK
+static void xenboot_write_console(struct console *console, const char *string,
+				  unsigned len)
+{
+	if (!xen_pv_domain())
+		return;
+
+	dom0_write_console(0, string, len);
+
+	if (xen_initial_domain())
+		return;
+
+	domU_write_early_console(string, len);
+}
+
 struct console xenboot_console = {
 	.name		= "xenboot",
 	.write		= xenboot_write_console,
@@ -664,3 +670,23 @@ void xen_raw_printk(const char *fmt, ...)
 
 	xen_raw_console_write(buf);
 }
+
+static void xenboot_earlycon_write(struct console *console,
+				  const char *string,
+				  unsigned len)
+{
+	dom0_write_console(0, string, len);
+
+	if (xen_initial_domain())
+		return;
+
+	domU_write_early_console(string, len);
+}
+
+static int __init xenboot_earlycon_setup(struct earlycon_device *device,
+					    const char *opt)
+{
+	device->con->write = xenboot_earlycon_write;
+	return 0;
+}
+EARLYCON_DECLARE(xenboot, xenboot_earlycon_setup);
-- 
1.7.10.4