PM/gxfb: add hook to PM console layer that allows disabling of suspend VT switch

Prior to suspend, we allocate and switch to a new VT; after suspend, we switch
back to the original VT.  This can be slow, and is completely unnecessary if
the framebuffer we're using can restore video properly.

This adds a hook that allows drivers to select whether or not to do this vt
switch, and changes the gxfb driver to call this hook.  It also adds a module
param to gxfb to allow controlling of the vt switch (defaulting to no switch).

(Note: I'm not convinced that console_sem is the best way to protect this, but
we should probably have some form of locking..)

[akpm@linux-foundation.org: build fix]
Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 1 deletions

diff --git a/kernel/power/console.c b/kernel/power/console.c
index 89bcf4973ee..b8628be2a46 100644
--- a/kernel/power/console.c
+++ b/kernel/power/console.c
@@ -7,17 +7,39 @@
 #include <linux/vt_kern.h>
 #include <linux/kbd_kern.h>
 #include <linux/console.h>
+#include <linux/module.h>
 #include "power.h"
 
 #if defined(CONFIG_VT) && defined(CONFIG_VT_CONSOLE)
 #define SUSPEND_CONSOLE	(MAX_NR_CONSOLES-1)
 
 static int orig_fgconsole, orig_kmsg;
+static int disable_vt_switch;
+
+/*
+ * Normally during a suspend, we allocate a new console and switch to it.
+ * When we resume, we switch back to the original console.  This switch
+ * can be slow, so on systems where the framebuffer can handle restoration
+ * of video registers anyways, there's little point in doing the console
+ * switch.  This function allows you to disable it by passing it '0'.
+ */
+void pm_set_vt_switch(int do_switch)
+{
+	acquire_console_sem();
+	disable_vt_switch = !do_switch;
+	release_console_sem();
+}
+EXPORT_SYMBOL(pm_set_vt_switch);
 
 int pm_prepare_console(void)
 {
 	acquire_console_sem();
 
+	if (disable_vt_switch) {
+		release_console_sem();
+		return 0;
+	}
+
 	orig_fgconsole = fg_console;
 
 	if (vc_allocate(SUSPEND_CONSOLE)) {
@@ -50,9 +72,12 @@ int pm_prepare_console(void)
 void pm_restore_console(void)
 {
 	acquire_console_sem();
+	if (disable_vt_switch) {
+		release_console_sem();
+		return;
+	}
 	set_console(orig_fgconsole);
 	release_console_sem();
 	kmsg_redirect = orig_kmsg;
-	return;
 }
 #endif