Messages in this thread | | | Date | Mon, 10 Mar 2008 17:44:24 -0400 | From | Andres Salomon <> | Subject | Re: [PATCH 6/6] PM/FB/gxfb: add config option that allows disabling of VT switch during suspend |
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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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