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..)

[[e-mail]: build fix]
Signed-off-by: Andres Salomon <[e-mail]>
Cc: Jordan Crouse <[e-mail]>
Cc: "Antonino A. Daplas" <[e-mail]>
Cc: Pavel Machek <[e-mail]>
Cc: "Rafael J. Wysocki" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/fb/gxfb.txt

···
 mode_option	- specify the video mode.  Of the form
 		  <x>x<y>[-<bpp>][@<refresh>]
 vram		- size of video ram (normally auto-detected)
-
+vt_switch	- enable vt switching during suspend/resume.  The vt
+		  switch is slow, but harmless.
 
 --
 Andres Salomon <[e-mail]>

drivers/video/geode/gxfb_core.c

···
 #include <linux/delay.h>
 #include <linux/fb.h>
 #include <linux/console.h>
+#include <linux/suspend.h>
 #include <linux/init.h>
 #include <linux/pci.h>
 #include <asm/geode.h>
···
 
 static char *mode_option;
 static int vram;
+static int vt_switch;
 
 /* Modes relevant to the GX (taken from modedb.c) */
 static const struct fb_videomode gx_modedb[] __initdata = {
···
 	gxfb_check_var(&info->var, info);
 	gxfb_set_par(info);
 
+	pm_set_vt_switch(vt_switch);
+
 	if (register_framebuffer(info) < 0) {
 		ret = -EINVAL;
 		goto err;
···
 
 module_param(vram, int, 0);
 MODULE_PARM_DESC(vram, "video memory size");
+
+module_param(vt_switch, int, 0);
+MODULE_PARM_DESC(vt_switch, "enable VT switch during suspend/resume");
 
 MODULE_DESCRIPTION("Framebuffer driver for the AMD Geode GX");
 MODULE_LICENSE("GPL");

include/linux/suspend.h

···
 #include <asm/errno.h>
 
 #if defined(CONFIG_PM_SLEEP) && defined(CONFIG_VT) && defined(CONFIG_VT_CONSOLE)
+extern void pm_set_vt_switch(int);
 extern int pm_prepare_console(void);
 extern void pm_restore_console(void);
 #else
-static inline int pm_prepare_console(void) { return 0; }
-static inline void pm_restore_console(void) {}
+static inline void pm_set_vt_switch(int do_switch)
+{
+}
+
+static inline int pm_prepare_console(void)
+{
+	return 0;
+}
+
+static inline void pm_restore_console(void)
+{
+}
 #endif
 
 typedef int __bitwise suspend_state_t;

kernel/power/console.c

···
 #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;
 
···
 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