[PATCH] PM: add config option that allows disabling of VT switch during suspend

[Andres Salomon]

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 CONFIG_DISABLE_SUSPEND_VT_SWITCH which allows the user to
select whether or not to do that switch.  This has been tested with the
gxfb driver (on a Geode GX dev board and OLPC prototype machines).  In
order for the user to even see this option, a framebuffer has to declare
support for it (via CONFIG_FBDEV_SUPPORTS_NOSWITCH).

Signed-off-by: Andres Salomon <dilinger@xxxxxxxxxx>
---
 drivers/char/Kconfig        |   21 +++++++++++++++++++++
 drivers/video/geode/Kconfig |    1 +
 include/linux/suspend.h     |    2 +-
 kernel/power/console.c      |    2 +-
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 47c6be8..7fe0e85 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -58,6 +58,27 @@ config VT_CONSOLE
 
 	  If unsure, say Y.
 
+config FBDEV_SUPPORTS_NOSWITCH
+	bool
+	default n
+
+config DISABLE_SUSPEND_VT_SWITCH
+	bool "Disable the console switch prior to suspend (EXPERIMENTAL)"
+	depends on VT_CONSOLE && PM && EXPERIMENTAL && FBDEV_SUPPORTS_NOSWITCH
+	default n
+	---help---
+	  This option disables the automatic switch to VT console that happens
+	  prior to Linux going into a suspend/sleep.  Your
+	  video card/framebuffer must be able to properly restore the
+	  display (even if X is doing something crazy!) in this scenario.
+	  This is useful for saving precious milliseconds during suspend and
+	  resume; however, if your framebuffer lacks support, it could leave
+	  your display in a weird state.  If you're even seeing this option,
+	  it means at least one of your selected framebuffer drivers supports
+	  restoring the display.
+
+	  If unsure, say N.
+
 config HW_CONSOLE
 	bool
 	depends on VT && !S390 && !UML
diff --git a/drivers/video/geode/Kconfig b/drivers/video/geode/Kconfig
index c5d8ba4..1497fe4 100644
--- a/drivers/video/geode/Kconfig
+++ b/drivers/video/geode/Kconfig
@@ -29,6 +29,7 @@ config FB_GEODE_GX
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select FBDEV_SUPPORTS_NOSWITCH
 	---help---
 	  Framebuffer driver for the display controller integrated into the
 	  AMD Geode GX processors.
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 1d7d4c5..46080f5 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -11,7 +11,7 @@
 #include <linux/mm.h>
 #include <asm/errno.h>
 
-#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_VT) && defined(CONFIG_VT_CONSOLE)
+#if defined(CONFIG_PM_SLEEP) && defined(CONFIG_VT) && defined(CONFIG_VT_CONSOLE) && !defined(CONFIG_DISABLE_SUSPEND_VT_SWITCH)
 extern int pm_prepare_console(void);
 extern void pm_restore_console(void);
 #else
diff --git a/kernel/power/console.c b/kernel/power/console.c
index 89bcf49..dca98f5 100644
--- a/kernel/power/console.c
+++ b/kernel/power/console.c
@@ -9,7 +9,7 @@
 #include <linux/console.h>
 #include "power.h"
 
-#if defined(CONFIG_VT) && defined(CONFIG_VT_CONSOLE)
+#if defined(CONFIG_VT) && defined(CONFIG_VT_CONSOLE) && !defined(CONFIG_DISABLE_SUSPEND_VT_SWITCH)
 #define SUSPEND_CONSOLE	(MAX_NR_CONSOLES-1)
 
 static int orig_fgconsole, orig_kmsg;
-- 
1.5.3.7

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