[RFC][PATCH 2/3] PM: Make console suspending configureable

["Rafael J. Wysocki" <rjw@sisk.pl>]

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>
---
 include/linux/console.h |    5 +++++
 kernel/power/Kconfig    |   11 +++++++++++
 kernel/printk.c         |    8 ++++++++
 3 files changed, 24 insertions(+)

Index: linux-2.6.18-rc4-mm1/include/linux/console.h
===================================================================
--- linux-2.6.18-rc4-mm1.orig/include/linux/console.h	2006-08-16 11:59:56.000000000 +0200
+++ linux-2.6.18-rc4-mm1/include/linux/console.h	2006-08-16 12:00:01.000000000 +0200
@@ -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
Index: linux-2.6.18-rc4-mm1/kernel/power/Kconfig
===================================================================
--- linux-2.6.18-rc4-mm1.orig/kernel/power/Kconfig	2006-08-16 11:59:56.000000000 +0200
+++ linux-2.6.18-rc4-mm1/kernel/power/Kconfig	2006-08-16 12:01:26.000000000 +0200
@@ -36,6 +36,17 @@ config PM_DEBUG
 	code. This is helpful when debugging and reporting various PM bugs, 
 	like suspend support.
 
+config PM_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
Index: linux-2.6.18-rc4-mm1/kernel/printk.c
===================================================================
--- linux-2.6.18-rc4-mm1.orig/kernel/printk.c	2006-08-16 11:59:56.000000000 +0200
+++ linux-2.6.18-rc4-mm1/kernel/printk.c	2006-08-16 12:08:59.000000000 +0200
@@ -702,6 +702,7 @@ int __init add_preferred_console(char *n
 	return 0;
 }
 
+#ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 /**
  * suspend_console - suspend the console subsystem
  *
@@ -709,8 +710,14 @@ int __init add_preferred_console(char *n
  */
 void suspend_console(void)
 {
+	printk("Suspending console(s)\n");
 	acquire_console_sem();
 	console_suspended = 1;
+	/* This is needed so that all of the messages that have already been
+	 * written to all consoles can be actually transmitted (eg. over a
+	 * network) before we try to suspend the consoles' devices.
+	 */
+	ssleep(2);
 }
 
 void resume_console(void)
@@ -718,6 +725,7 @@ 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.