printk: add console_suspend module parameter

We are enabling some power features on medfield.  To test suspend-2-RAM
conveniently, we need turn on/off console_suspend_enabled frequently.

Add a module parameter, so users could change it by:
/sys/module/printk/parameters/console_suspend

Signed-off-by: Yanmin Zhang <yanmin_zhang@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/kernel-parameters.txt

@@ -1669,6 +1669,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			debugging driver suspend/resume hooks).  This may
 			not work reliably with all consoles, but is known
 			to work with serial and VGA consoles.
+			To facilitate more flexible debugging, we also add
+			console_suspend, a printk module parameter to control
+			it. Users could use console_suspend (usually
+			/sys/module/printk/parameters/console_suspend) to
+			turn on/off it dynamically.
 
 	noaliencache	[MM, NUMA, SLAB] Disables the allocation of alien
 			caches in the slab allocator.  Saves per-node memory,

kernel/printk.c

@@ -1111,6 +1111,10 @@ static int __init console_suspend_disable(char *str)
 	return 1;
 }
 __setup("no_console_suspend", console_suspend_disable);
+module_param_named(console_suspend, console_suspend_enabled,
+		bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
+	" and hibernate operations");
 
 /**
  * suspend_console - suspend the console subsystem