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

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

[Andres Salomon]

This is purely for suspend/resume time optimization.


From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
From: Andres Salomon <dilinger@debian.org>
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 <dilinger@debian.org>
---
 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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Re: [PATCH 6/6] PM/FB/gxfb: add config option that allows disabling of VT switch during suspend

[Andrew Morton]

On Sat, 8 Mar 2008 20:49:27 -0500
Andres Salomon <dilinger@queued.net> wrote:

> This is purely for suspend/resume time optimization.
> 
> 
> >From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
> From: Andres Salomon <dilinger@debian.org>
> 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 <dilinger@debian.org>
> ---
>  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.

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


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

[Andres Salomon]

On Mon, 10 Mar 2008 14:19:39 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Sat, 8 Mar 2008 20:49:27 -0500
> Andres Salomon <dilinger@queued.net> wrote:
> 
> > This is purely for suspend/resume time optimization.
> > 
> > 
> > >From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
> > From: Andres Salomon <dilinger@debian.org>
> > 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 <dilinger@debian.org>
> > ---
> >  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.
> 
> 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..



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

[Andrew Morton]

On Mon, 10 Mar 2008 17:44:24 -0400
Andres Salomon <dilinger@queued.net> wrote:

> On Mon, 10 Mar 2008 14:19:39 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > 
> > 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..
> 

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?


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

[Andres Salomon]

On Mon, 10 Mar 2008 14:51:18 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 10 Mar 2008 17:44:24 -0400
> Andres Salomon <dilinger@queued.net> wrote:
> 
> > On Mon, 10 Mar 2008 14:19:39 -0700
> > Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > 
> > > 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..
> > 
> 
> 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..



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

[Jordan Crouse]

On 10/03/08 18:14 -0400, Andres Salomon wrote:
> On Mon, 10 Mar 2008 14:51:18 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Mon, 10 Mar 2008 17:44:24 -0400
> > Andres Salomon <dilinger@queued.net> wrote:
> > 
> > > On Mon, 10 Mar 2008 14:19:39 -0700
> > > Andrew Morton <akpm@linux-foundation.org> wrote:
> > > 
> > > > 
> > > > 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..
> > > 
> > 
> > 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..

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

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


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

[Pavel Machek]

Hi!

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

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

[Rafael J. Wysocki]

On Monday, 10 of March 2008, Andres Salomon wrote:
> On Mon, 10 Mar 2008 14:51:18 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Mon, 10 Mar 2008 17:44:24 -0400
> > Andres Salomon <dilinger@queued.net> wrote:
> > 
> > > On Mon, 10 Mar 2008 14:19:39 -0700
> > > Andrew Morton <akpm@linux-foundation.org> wrote:
> > > 
> > > > 
> > > > 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..
> > > 
> > 
> > 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..

FWIW, I prefer the original .config option idea.

Thanks,
Rafael

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

[Andrew Morton]

On Mon, 10 Mar 2008 23:28:18 +0100 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> > > > 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..
> 
> FWIW, I prefer the original .config option idea.

Please explain your reasoning?

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

[Andrew Morton]

On Mon, 10 Mar 2008 18:14:46 -0400 Andres Salomon <dilinger@queued.net> wrote:

> On Mon, 10 Mar 2008 14:51:18 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Mon, 10 Mar 2008 17:44:24 -0400
> > Andres Salomon <dilinger@queued.net> wrote:
> > 
> > > On Mon, 10 Mar 2008 14:19:39 -0700
> > > Andrew Morton <akpm@linux-foundation.org> wrote:
> > > 
> > > > 
> > > > 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..
> > > 
> > 
> > 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?

>  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.



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

[Pavel Machek]

On Mon 2008-03-10 14:19:39, Andrew Morton wrote:
> On Sat, 8 Mar 2008 20:49:27 -0500
> Andres Salomon <dilinger@queued.net> wrote:
> 
> > This is purely for suspend/resume time optimization.
> > 
> > 
> > >From 874aa20022a2501a30704163ed31a7baba7de9e5 Mon Sep 17 00:00:00 2001
> > From: Andres Salomon <dilinger@debian.org>
> > 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).
...
> 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
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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