[PATCH] Provide console_suspend() and console_resume()

Add console_stop() and console_start() methods so the serial drivers
can disable console output before suspending a port, and re-enable output
afterwards.

We also add locking to ensure that we synchronise with any in-progress
printk.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/serial/serial_core.c

@@ -1923,7 +1923,7 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *port)
 	 * Disable the console device before suspending.
 	 */
 	if (uart_console(port))
-		port->cons->flags &= ~CON_ENABLED;
+		console_stop(port->cons);
 
 	uart_change_pm(state, 3);
 
@@ -1945,7 +1945,7 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *port)
 	 */
 	if (uart_console(port)) {
 		uart_change_speed(state, NULL);
-		port->cons->flags |= CON_ENABLED;
+		console_start(port->cons);
 	}
 
 	if (state->info && state->info->flags & UIF_INITIALIZED) {

include/linux/console.h

@@ -105,6 +105,8 @@ extern void release_console_sem(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
 extern struct tty_driver *console_device(int *);
+extern void console_stop(struct console *);
+extern void console_start(struct console *);
 extern int is_console_locked(void);
 
 /* Some debug stub to catch some of the obvious races in the VT code */

kernel/printk.c

@@ -703,6 +703,27 @@ struct tty_driver *console_device(int *index)
 	return driver;
 }
 
+/*
+ * Prevent further output on the passed console device so that (for example)
+ * serial drivers can disable console output before suspending a port, and can
+ * re-enable output afterwards.
+ */
+void console_stop(struct console *console)
+{
+	acquire_console_sem();
+	console->flags &= ~CON_ENABLED;
+	release_console_sem();
+}
+EXPORT_SYMBOL(console_stop);
+
+void console_start(struct console *console)
+{
+	acquire_console_sem();
+	console->flags |= CON_ENABLED;
+	release_console_sem();
+}
+EXPORT_SYMBOL(console_start);
+
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to