Add a flag indicating when the serial console is ready

For sandbox we have a fallback console which is used very early in
U-Boot, before serial drivers are available. Rather than try to guess
when to switch to the real console, add a flag so we can be sure. This
makes sure that sandbox can always output a panic() message, for example,
and avoids silent failure (which is very annoying in sandbox).

Signed-off-by: Simon Glass <sjg@chromium.org>

common/console.c

@@ -417,7 +417,7 @@ static inline void print_pre_console_buffer(void) {}
 void putc(const char c)
 {
 #ifdef CONFIG_SANDBOX
-	if (!gd) {
+	if (!gd || !(gd->flags & GD_FLG_SERIAL_READY)) {
 		os_putc(c);
 		return;
 	}
@@ -447,7 +447,7 @@ void putc(const char c)
 void puts(const char *s)
 {
 #ifdef CONFIG_SANDBOX
-	if (!gd) {
+	if (!gd || !(gd->flags & GD_FLG_SERIAL_READY)) {
 		os_puts(s);
 		return;
 	}

drivers/serial/serial.c

@@ -418,6 +418,7 @@ static struct serial_device *get_current(void)
  */
 int serial_init(void)
 {
+	gd->flags |= GD_FLG_SERIAL_READY;
 	return get_current()->start();
 }
 

include/asm-generic/global_data.h

@@ -106,5 +106,6 @@ typedef struct global_data {
 #define GD_FLG_LOGINIT		0x00020	/* Log Buffer has been initialized */
 #define GD_FLG_DISABLE_CONSOLE	0x00040	/* Disable console (in & out)	   */
 #define GD_FLG_ENV_READY	0x00080	/* Env. imported into hash table   */
+#define GD_FLG_SERIAL_READY	0x00100	/* Pre-reloc serial console ready  */
 
 #endif /* __ASM_GENERIC_GBL_DATA_H */