[RFC 4/6] xen/console: Add support for early printk

[Julien Grall <julien.grall@linaro.org>]

On ARM, a function (early_printk) was introduced to output message when the
serial port is not initialized.

This solution is fragile because the developper needs to know when the serial
port is initialized, to use either early_printk or printk. Moreover some
functions (mainly in common code), only use printk. This will result to a loss
of message sometimes.

Directly call early_printk in console code when the serial port is not yet
initialized. For this purpose use serial_steal_fn.

Cc: Keir Fraser <keir@xen.org>
Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
 xen/drivers/char/console.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 532c426..f83c92e 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -28,6 +28,9 @@
 #include <asm/debugger.h>
 #include <asm/div64.h>
 #include <xen/hypercall.h> /* for do_console_io */
+#ifdef CONFIG_EARLY_PRINTK
+#include <asm/early_printk.h>
+#endif
 
 /* console: comma-separated list of console outputs. */
 static char __initdata opt_console[30] = OPT_CONSOLE_STR;
@@ -245,7 +248,12 @@ long read_console_ring(struct xen_sysctl_readconsole *op)
 static char serial_rx_ring[SERIAL_RX_SIZE];
 static unsigned int serial_rx_cons, serial_rx_prod;
 
-static void (*serial_steal_fn)(const char *);
+#ifndef CONFIG_EARLY_PRINTK
+static inline void early_puts(const char *str)
+{}
+#endif
+
+static void (*serial_steal_fn)(const char *) = early_puts;
 
 int console_steal(int handle, void (*fn)(const char *))
 {
@@ -652,7 +660,10 @@ void __init console_init_preirq(void)
         else if ( !strncmp(p, "none", 4) )
             continue;
         else if ( (sh = serial_parse_handle(p)) >= 0 )
+        {
             sercon_handle = sh;
+            serial_steal_fn = NULL;
+        }
         else
         {
             char *q = strchr(p, ',');
-- 
1.8.3.1