[PATCH 4/4] serial: serial_xen: add DEBUG_UART support

[AKASHI Takahiro]

By using a hypervisor call, we can implement DEBUG_UART on xen.
This will allow us to see messages even earlier than serial_init().

Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
 drivers/serial/Kconfig      | 14 +++++++++++---
 drivers/serial/serial_xen.c | 20 ++++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index e344677f91f6..536cf0641773 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -401,11 +401,19 @@ config DEBUG_UART_MTK
 	  driver will be available until the real driver model serial is
 	  running.
 
+config DEBUG_UART_XEN
+	bool "XEN Hypervisor Console"
+	depends on XEN_SERIAL
+	help
+	  Select this to enable a debug UART using the serial_xen driver. You
+	  will not have to provide any parameters to make this work. The driver
+          will be available until the real driver-model serial is running.
+
 endchoice
 
 config DEBUG_UART_BASE
 	hex "Base address of UART"
-	depends on DEBUG_UART
+	depends on DEBUG_UART && !DEBUG_UART_XEN
 	default 0 if DEBUG_UART_SANDBOX
 	help
 	  This is the base address of your UART for memory-mapped UARTs.
@@ -415,7 +423,7 @@ config DEBUG_UART_BASE
 
 config DEBUG_UART_CLOCK
 	int "UART input clock"
-	depends on DEBUG_UART
+	depends on DEBUG_UART && !DEBUG_UART_XEN
 	default 0 if DEBUG_UART_SANDBOX
 	help
 	  The UART input clock determines the speed of the internal UART
@@ -427,7 +435,7 @@ config DEBUG_UART_CLOCK
 
 config DEBUG_UART_SHIFT
 	int "UART register shift"
-	depends on DEBUG_UART
+	depends on DEBUG_UART && !DEBUG_UART_XEN
 	default 0 if DEBUG_UART
 	help
 	  Some UARTs (notably ns16550) support different register layouts
diff --git a/drivers/serial/serial_xen.c b/drivers/serial/serial_xen.c
index ed191829f059..34c90ece40fc 100644
--- a/drivers/serial/serial_xen.c
+++ b/drivers/serial/serial_xen.c
@@ -5,6 +5,7 @@
  */
 #include <common.h>
 #include <cpu_func.h>
+#include <debug_uart.h>
 #include <dm.h>
 #include <serial.h>
 #include <watchdog.h>
@@ -15,11 +16,14 @@
 #include <xen/events.h>
 
 #include <xen/interface/sched.h>
+#include <xen/interface/xen.h>
 #include <xen/interface/hvm/hvm_op.h>
 #include <xen/interface/hvm/params.h>
 #include <xen/interface/io/console.h>
 #include <xen/interface/io/ring.h>
 
+#include <asm/xen/hypercall.h>
+
 DECLARE_GLOBAL_DATA_PTR;
 
 u32 console_evtchn;
@@ -178,3 +182,19 @@ U_BOOT_DRIVER(serial_xen) = {
 	.flags			= DM_FLAG_PRE_RELOC,
 };
 
+#if defined(CONFIG_DEBUG_UART_XEN)
+static inline void _debug_uart_init(void) {}
+
+static inline void _debug_uart_putc(int c)
+{
+#if CONFIG_IS_ENABLED(ARM)
+	xen_debug_putc(c);
+#else
+	/* the type cast should work on LE only */
+	HYPERVISOR_console_io(CONSOLEIO_write, 1, (char *)&ch);
+#endif
+}
+
+DEBUG_UART_FUNCS
+
+#endif
-- 
2.28.0