linux-kernel - Re: [PATCH 6/7] pm: Config option to disable handling of console during suspend/resume

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Date:	Tue, 29 Jul 2008 21:47:16 -0700
From:	Greg KH <greg@...ah.com>
To:	Ben Collins <ben.collins@...onical.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH 6/7] pm: Config option to disable handling of console
	during suspend/resume

On Tue, Jul 29, 2008 at 05:51:50PM -0400, Ben Collins wrote:
> On Tue, 2008-07-29 at 23:15 +0200, Rafael J. Wysocki wrote:
> > On Tuesday, 29 of July 2008, Greg KH wrote:
> > > On Sun, Jul 20, 2008 at 09:48:28PM -0400, Ben Collins wrote:
> > > > Config option allows userspace to handle console during suspend/resume
> > > > instead of the kernel.
> > > > 
> > > > Signed-off-by: Ben Collins <ben.collins@...onical.com>
> > > > ---
> > > >  kernel/power/Kconfig   |   15 +++++++++++++++
> > > >  kernel/power/console.c |    4 ++++
> > > >  2 files changed, 19 insertions(+), 0 deletions(-)
> > > > 
> > > > diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> > > > index b45da40..6855299 100644
> > > > --- a/kernel/power/Kconfig
> > > > +++ b/kernel/power/Kconfig
> > > > @@ -105,6 +105,21 @@ config SUSPEND_FREEZER
> > > >  
> > > >  	  Turning OFF this setting is NOT recommended! If in doubt, say Y.
> > > >  
> > > > +config PM_DISABLE_CONSOLE
> > > > +	bool "Disable Power Management messing with the active console"
> > > > +	depends on PM
> > > > +	default n
> > > > +	---help---
> > > > +	  By default, PM will take over the active console (generally, this means
> > > > +	  switching to the console when suspending from X). This can at times cause
> > > > +	  problems, especially if userspace suspend scripts try to do things with
> > > > +	  the console before or after suspending (e.g. calling vbestate).
> > > > +
> > > > +	  To work around this, enable this option so that PM will not handle the
> > > > +	  console.
> > > > +
> > > > +	  If unsure, say N.
> > > > +
> > > >  config HIBERNATION
> > > >  	bool "Hibernation (aka 'suspend to disk')"
> > > >  	depends on PM && SWAP && ARCH_HIBERNATION_POSSIBLE
> > > > diff --git a/kernel/power/console.c b/kernel/power/console.c
> > > > index b8628be..8b9706f 100644
> > > > --- a/kernel/power/console.c
> > > > +++ b/kernel/power/console.c
> > > > @@ -33,6 +33,7 @@ EXPORT_SYMBOL(pm_set_vt_switch);
> > > >  
> > > >  int pm_prepare_console(void)
> > > >  {
> > > > +#ifndef CONFIG_PM_DISABLE_CONSOLE
> > > 
> > > Can't you do this in a .h file instead?
> > > 
> > > And is this really needed?  Why has no other distro needed this change?
> > > What is so wierd about your suspend setup to require this?
> > 
> > Reportedly, some systems have problems with graphics restoration from user
> > space if the switch is done.
> > 
> > Anyway, I'd prefer to use the (already existing) pm_set_vt_switch() thing for
> > that, maybe with the help of a command line parameter, to adding the .config
> > option like this.
> 
> Ah. I didn't notice pm_set_vt_switch(). Then what I would like better is
> the config option to set a default. For us, not doing the vt switch is a
> good default (I don't think we have a case where suspend/resume requires
> it).
> 
> Something like:
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index e7bea3e..6a042f8 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2247,6 +2247,11 @@ and is between 256 and 4096 characters. It is defined in the file
>  	vmpoff=		[KNL,S390] Perform z/VM CP command after power off.
>  			Format: <command>
>  
> +	vt_switch=	[PM] Switch vt's during suspend/resume
> +			Format: { 0 | 1 }
> +			Default is normally '1', but depends on value of
> +			the PM_DISABLE_CONSOLE config option.
> +

Why a build time config option?  Why not just set the command line
option if you need this?  And/or make it a sysctrl?

That way we don't have to add yet-another-config-option for distros and
users to get wrong.

thanks,

greg k-h
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