[PATCH] PM: make it possible to disable console suspending

Change suspend_console() so that it waits for all consoles to flush the
remaining messages and make it possible to switch the console suspending off
with the help of a Kconfig option.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Stefan Seyfried <seife@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/console.h

@@ -120,9 +120,14 @@ extern void console_stop(struct console *);
 extern void console_start(struct console *);
 extern int is_console_locked(void);
 
+#ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 /* Suspend and resume console messages over PM events */
 extern void suspend_console(void);
 extern void resume_console(void);
+#else
+static inline void suspend_console(void) {}
+static inline void resume_console(void) {}
+#endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 
 /* Some debug stub to catch some of the obvious races in the VT code */
 #if 1

kernel/power/Kconfig

@@ -36,6 +36,17 @@ config PM_DEBUG
 	code. This is helpful when debugging and reporting various PM bugs, 
 	like suspend support.
 
+config DISABLE_CONSOLE_SUSPEND
+	bool "Keep console(s) enabled during suspend/resume (DANGEROUS)"
+	depends on PM && PM_DEBUG
+	default n
+	---help---
+	This option turns off the console suspend mechanism that prevents
+	debug messages from reaching the console during the suspend/resume
+	operations.  This may be helpful when debugging device drivers'
+	suspend/resume routines, but may itself lead to problems, for example
+	if netconsole is used.
+
 config PM_TRACE
 	bool "Suspend/resume event tracing"
 	depends on PM && PM_DEBUG && X86_32 && EXPERIMENTAL

kernel/printk.c

@@ -721,13 +721,15 @@ int __init add_preferred_console(char *name, int idx, char *options)
 	return 0;
 }
 
+#ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 /**
  * suspend_console - suspend the console subsystem
  *
  * This disables printk() while we go into suspend states
  */
 void suspend_console(void)
 {
+	printk("Suspending console(s)\n");
 	acquire_console_sem();
 	console_suspended = 1;
 }
@@ -737,6 +739,7 @@ void resume_console(void)
 	console_suspended = 0;
 	release_console_sem();
 }
+#endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 
 /**
  * acquire_console_sem - lock the console system for exclusive use.