PM/FB/gxfb: add config option that allows disabling of VT switch during suspend

PATCH In review Andres Salomon 5 participants 11 messages Mar 9, 2008 – Mar 10, 2008

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Andres Salomon

author

2008-03-09 01:45 UTC #0 lore raw

PATCH 6/6 PM/FB/gxfb: add config option that allows disabling of VT switch during suspend

This is purely for suspend/resume time optimization.

From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
From: Andres Salomon <[email protected]>
Date: Wed, 5 Mar 2008 16:40:25 -0500
Subject: [PATCH] PM: add config option that allows disabling of VT switch during suspend

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 <[email protected]>

---
 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(-)

drivers/char/Kconfig +21 -0

index 47c6be8..7fe0e85 100644
@@ -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

drivers/video/geode/Kconfig +1 -0

index c5d8ba4..1497fe4 100644
@@ -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.

include/linux/suspend.h +1 -1

index 1d7d4c5..46080f5 100644
@@ -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

kernel/power/console.c +1 -1

index 89bcf49..dca98f5 100644
@@ -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;

Signature · 7 lines

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Andrew Morton

2008-03-10 21:25 UTC #1 lore raw

Quoted 44 lines · On Sat, 8 Mar 2008 20:49:27 -0500 Andres Salomon <[email protected]> wrote:

This is purely for suspend/resume time optimization.
Quoted 1 line
From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
From: Andres Salomon <[email protected]>
Date: Wed, 5 Mar 2008 16:40:25 -0500
Subject: [PATCH] PM: add config option that allows disabling of VT switch during suspend
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 <[email protected]>
---
 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(-)
drivers/char/Kconfig +10 -0
index 47c6be8..7fe0e85 100644
@@ -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

drivers/char/Kconfig config VT_CONSOLE · line 80

Quoted 10 lines

drivers/char/Kconfig +10 -0

+	  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.

It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.

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Andres Salomon

author

2008-03-10 21:40 UTC #2 lore raw

Quoted 52 lines · On Mon, 10 Mar 2008 14:19:39 -0700 Andrew Morton <[email protected]>…

Quoted 49 lines · On Sat, 8 Mar 2008 20:49:27 -0500 Andres Salomon <[email protected]> wrote:
This is purely for suspend/resume time optimization.
Quoted 1 line
From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
From: Andres Salomon <[email protected]>
Date: Wed, 5 Mar 2008 16:40:25 -0500
Subject: [PATCH] PM: add config option that allows disabling of VT switch during suspend
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 <[email protected]>
---
 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(-)
drivers/char/Kconfig +15 -0
index 47c6be8..7fe0e85 100644
@@ -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

Quoted 9 lines

drivers/char/Kconfig config VT_CONSOLE · line 80
Quoted 5 lines
drivers/char/Kconfig +5 -0
+	  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.
It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.

Well, it shouldn't be supported at _all_ unless the framebuffer driver supports it; you're asking for it to be converted to something like the following?

#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
static int no_vt_switch;
#endif

int pm_prepare_console(void)
{

#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
	if (no_vt_switch)
		return 0;
#endif
	...
}

#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
module_param(no_vt_switch, int, 0);
MODULE_PARM_DESC(no_vt_switch, "...");
#endif

If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..

Andrew Morton

2008-03-10 21:52 UTC #3 lore raw

Quoted 33 lines · On Mon, 10 Mar 2008 17:44:24 -0400 Andres Salomon <[email protected]> wrote:

Quoted 4 lines · On Mon, 10 Mar 2008 14:19:39 -0700 Andrew Morton <[email protected]>…
It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.
Well, it shouldn't be supported at _all_ unless the framebuffer driver supports it; you're asking for it to be converted to something like the following?
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
static int no_vt_switch;
#endif
int pm_prepare_console(void)
{
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
	if (no_vt_switch)
		return 0;
#endif
	...
}
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
module_param(no_vt_switch, int, 0);
MODULE_PARM_DESC(no_vt_switch, "...");
#endif

Quoted 4 lines

If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..

I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?

Andres Salomon

author

2008-03-10 22:11 UTC #4 lore raw

Quoted 36 lines · On Mon, 10 Mar 2008 14:51:18 -0700 Andrew Morton <[email protected]>…

Quoted 33 lines · On Mon, 10 Mar 2008 17:44:24 -0400 Andres Salomon <[email protected]> wrote:
Quoted 4 lines · On Mon, 10 Mar 2008 14:19:39 -0700 Andrew Morton <[email protected]>…
It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.
Well, it shouldn't be supported at _all_ unless the framebuffer driver supports it; you're asking for it to be converted to something like the following?
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
static int no_vt_switch;
#endif
int pm_prepare_console(void)
{
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
	if (no_vt_switch)
		return 0;
#endif
	...
}
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
module_param(no_vt_switch, int, 0);
MODULE_PARM_DESC(no_vt_switch, "...");
#endif

Quoted 9 lines

Quoted 4 lines
If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..
I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?

That's a possibility, but doesn't adding hooks into PM core for two drivers (lxfb and gxfb) seems like overkill? I also don't really see anyone needing to switch back and forth between VT_SWITCH and NO_VT_SWITCH other than to work around possible bugs in the register save/restore code..

Jordan Crouse

2008-03-10 22:26 UTC #5 lore raw

Quoted 49 lines · Andres Salomon

Quoted 36 lines · On Mon, 10 Mar 2008 14:51:18 -0700 Andrew Morton <[email protected]>…
Quoted 33 lines · On Mon, 10 Mar 2008 17:44:24 -0400 Andres Salomon <[email protected]> wrote:
Quoted 4 lines · On Mon, 10 Mar 2008 14:19:39 -0700 Andrew Morton <[email protected]>…
It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.
Well, it shouldn't be supported at _all_ unless the framebuffer driver supports it; you're asking for it to be converted to something like the following?
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
static int no_vt_switch;
#endif
int pm_prepare_console(void)
{
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
	if (no_vt_switch)
		return 0;
#endif
	...
}
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
module_param(no_vt_switch, int, 0);
MODULE_PARM_DESC(no_vt_switch, "...");
#endif
Quoted 9 lines
Quoted 4 lines
If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..
I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?

Quoted 5 lines

That's a possibility, but doesn't adding hooks into PM core for two drivers (lxfb and gxfb) seems like overkill? I also don't really see anyone needing to switch back and forth between VT_SWITCH and NO_VT_SWITCH other than to work around possible bugs in the register save/restore code..

I like Andrew's idea. I wager This won't be Geode specific for long. Either other drivers will get the hint and add real save/restore code or the GPU subystem code being worked on by the X folks will come along and make the VT switch obsolete for everybody. Either way, I see hooks in the PM core as generic love that everybody can benefit from.

Jordan

Signature · 9 lines

Jordan Crouse
Systems Software Development Engineer 
Advanced Micro Devices, Inc.


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Pavel Machek

2008-03-10 23:05 UTC #6 lore raw

Hi!

Quoted 16 lines

Quoted 10 lines
Quoted 9 lines
Quoted 4 lines
If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..
I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?
Quoted 5 lines
That's a possibility, but doesn't adding hooks into PM core for two drivers (lxfb and gxfb) seems like overkill? I also don't really see anyone needing to switch back and forth between VT_SWITCH and NO_VT_SWITCH other than to work around possible bugs in the register save/restore code..

Quoted 5 lines

I like Andrew's idea. I wager This won't be Geode specific for long. Either other drivers will get the hint and add real save/restore code or the GPU subystem code being worked on by the X folks will come along and make the VT switch obsolete for everybody. Either way, I see hooks in the PM core as generic love that everybody can benefit from.

Exactly. We'd like _all_ drivers to behave like this.

Signature · 7 lines

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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Rafael J. Wysocki

2008-03-10 22:29 UTC #7 lore raw

In reply to Andres Salomon

Quoted 49 lines · Andres Salomon

Quoted 36 lines · On Mon, 10 Mar 2008 14:51:18 -0700 Andrew Morton <[email protected]>…
Quoted 33 lines · On Mon, 10 Mar 2008 17:44:24 -0400 Andres Salomon <[email protected]> wrote:
Quoted 4 lines · On Mon, 10 Mar 2008 14:19:39 -0700 Andrew Morton <[email protected]>…
It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.
Well, it shouldn't be supported at _all_ unless the framebuffer driver supports it; you're asking for it to be converted to something like the following?
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
static int no_vt_switch;
#endif
int pm_prepare_console(void)
{
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
	if (no_vt_switch)
		return 0;
#endif
	...
}
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
module_param(no_vt_switch, int, 0);
MODULE_PARM_DESC(no_vt_switch, "...");
#endif
Quoted 9 lines
Quoted 4 lines
If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..
I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?

Quoted 5 lines

That's a possibility, but doesn't adding hooks into PM core for two drivers (lxfb and gxfb) seems like overkill? I also don't really see anyone needing to switch back and forth between VT_SWITCH and NO_VT_SWITCH other than to work around possible bugs in the register save/restore code..

FWIW, I prefer the original .config option idea.

Thanks,
Rafael

Andrew Morton

2008-03-10 23:37 UTC #8 lore raw

Quoted 10 lines · On Mon, 10 Mar 2008 23:28:18 +0100 "Rafael J. Wysocki" <[email protected]> wrote:

Quoted 10 lines
Quoted 9 lines
Quoted 4 lines
If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..
I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?

Quoted 7 lines

Quoted 5 lines
That's a possibility, but doesn't adding hooks into PM core for two drivers (lxfb and gxfb) seems like overkill? I also don't really see anyone needing to switch back and forth between VT_SWITCH and NO_VT_SWITCH other than to work around possible bugs in the register save/restore code..
FWIW, I prefer the original .config option idea.

Please explain your reasoning?

Andrew Morton

2008-03-10 22:30 UTC #9 lore raw

In reply to Andres Salomon

Quoted 44 lines · On Mon, 10 Mar 2008 18:14:46 -0400 Andres Salomon <[email protected]> wrote:

Quoted 41 lines · On Mon, 10 Mar 2008 14:51:18 -0700 Andrew Morton <[email protected]>…
Quoted 37 lines · On Mon, 10 Mar 2008 17:44:24 -0400 Andres Salomon <[email protected]> wrote:
Quoted 4 lines · On Mon, 10 Mar 2008 14:19:39 -0700 Andrew Morton <[email protected]>…
It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.
Well, it shouldn't be supported at _all_ unless the framebuffer driver supports it; you're asking for it to be converted to something like the following?
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
static int no_vt_switch;
#endif
int pm_prepare_console(void)
{
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
	if (no_vt_switch)
		return 0;
#endif
	...
}
#ifdef CONFIG_FBDEV_SUPPORTS_NOSWITCH
module_param(no_vt_switch, int, 0);
MODULE_PARM_DESC(no_vt_switch, "...");
#endif
If so, that means extra #ifdef's sprinkled throughout the code. Note that most framebuffer drivers won't be supporting this, and those that do will almost certainly always want vt switching turned off..

Quoted 7 lines

Quoted 4 lines
I don't think you need any ifdefs or config options at all, do you? Just add a new module parameter to this driver and some little interface into the PM core which allows the driver to set no_vt_switch?
That's a possibility, but doesn't adding hooks into PM core for two drivers (lxfb and gxfb) seems like overkill?

It's just a few bytes of code?

Quoted 4 lines

I also don't really see
anyone needing to switch back and forth between VT_SWITCH and NO_VT_SWITCH other than to work around possible bugs in the register save/restore code..

Making driver behaviour depend upon compile-time settings is really to be avoided. A distributor has to choose one setting or the other, and a) that means that some people will get the wrong setting and b) there's a decent chance that the distributor will get it wrong.

Pavel Machek

2008-03-10 23:04 UTC #10 lore raw

In reply to Andrew Morton

Quoted 20 lines · Andrew Morton

Quoted 17 lines · On Sat, 8 Mar 2008 20:49:27 -0500 Andres Salomon <[email protected]> wrote:
This is purely for suspend/resume time optimization.
Quoted 1 line
From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
From: Andres Salomon <[email protected]>
Date: Wed, 5 Mar 2008 16:40:25 -0500
Subject: [PATCH] PM: add config option that allows disabling of VT switch during suspend
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).

...

Quoted 2 lines

It would be far preferable to do this via a kernel boot parameter rather than via a kernel rebuild.

Actually, it would be better to get this right automatically, without any config options.

And no, this is not only gxfb/lxfb. At least Sharp Zaurus and FIC neo1973 can suspend without switching consoles...
Pavel

Signature · 7 lines

(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/