serial: convert early_uart to earlycon for 8250

Beacuse SERIAL_PORT_DFNS is removed from include/asm-i386/serial.h and
include/asm-x86_64/serial.h.  the serial8250_ports need to be probed late in
serial initializing stage.  the console_init=>serial8250_console_init=>
register_console=>serial8250_console_setup will return -ENDEV, and console
ttyS0 can not be enabled at that time.  need to wait till uart_add_one_port in
drivers/serial/serial_core.c to call register_console to get console ttyS0.
that is too late.

Make early_uart to use early_param, so uart console can be used earlier.  Make
it to be bootconsole with CON_BOOT flag, so can use console handover feature.
and it will switch to corresponding normal serial console automatically.

new command line will be:
	console=uart8250,io,0x3f8,9600n8
	console=uart8250,mmio,0xff5e0000,115200n8
or
	earlycon=uart8250,io,0x3f8,9600n8
	earlycon=uart8250,mmio,0xff5e0000,115200n8

it will print in very early stage:
	Early serial console at I/O port 0x3f8 (options '9600n8')
	console [uart0] enabled
later for console it will print:
	console handover: boot [uart0] -> real [ttyS0]

Signed-off-by: <yinghai.lu@sun.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 7ce9a8c..f46cc6d 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -726,6 +726,25 @@ int __init add_preferred_console(char *name, int idx, char *options)
 	return 0;
 }
 
+int __init update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
+{
+	struct console_cmdline *c;
+	int i;
+
+	for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
+		if (strcmp(console_cmdline[i].name, name) == 0 &&
+			  console_cmdline[i].index == idx) {
+				c = &console_cmdline[i];
+				memcpy(c->name, name_new, sizeof(c->name));
+				c->name[sizeof(c->name) - 1] = 0;
+				c->options = options;
+				c->index = idx_new;
+				return i;
+		}
+	/* not found */
+	return -1;
+}
+
 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 /**
  * suspend_console - suspend the console subsystem
@@ -942,6 +961,9 @@ void register_console(struct console *console)
 	if (preferred_console < 0 || bootconsole || !console_drivers)
 		preferred_console = selected_console;
 
+	if (console->early_setup)
+		console->early_setup();
+
 	/*
 	 *	See if we want to use this console driver. If we
 	 *	didn't select a console we take the first one