[Intel-gfx] [PATCH] PM: make VT switching to the suspend console optional v2

[Rafael J. Wysocki]

On Saturday, February 02, 2013 04:34:08 PM Jesse Barnes wrote:
> KMS drivers can potentially restore the display configuration without
> userspace help.  Such drivers can can call a new funciton,
> pm_vt_switch_required(false) if they support this feature.  In that
> case, the PM layer won't VT switch to the suspend console at suspend
> time and then back to the original VT on resume, but rather leave things
> alone for a nicer looking suspend and resume sequence.
> 
> v2: make a function so we can handle multiple drivers (Alan)
> 
> Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> ---
>  include/linux/pm.h     |    2 ++
>  kernel/power/console.c |   59 ++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 61 insertions(+)
> 
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 03d7bb1..5c2b131 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -35,6 +35,8 @@ extern void (*pm_idle)(void);
>  extern void (*pm_power_off)(void);
>  extern void (*pm_power_off_prepare)(void);
>  
> +extern void pm_vt_switch_required(bool required);
> +
>  /*
>   * Device power management
>   */
> diff --git a/kernel/power/console.c b/kernel/power/console.c
> index b1dc456..67c4de3 100644
> --- a/kernel/power/console.c
> +++ b/kernel/power/console.c
> @@ -4,6 +4,7 @@
>   * Originally from swsusp.
>   */
>  
> +#include <linux/console.h>
>  #include <linux/vt_kern.h>
>  #include <linux/kbd_kern.h>
>  #include <linux/vt.h>
> @@ -14,8 +15,63 @@
>  
>  static int orig_fgconsole, orig_kmsg;
>  
> +DEFINE_SPINLOCK(vt_switch_lock);
> +static int vt_switch_required = -1;
> +
> +/**
> + * pm_vt_switch_required - indicate VT switch at suspend requirements
> + * @required: if true, caller needs VT switch at suspend/resume time
> + *
> + * The different console drivers may or may not require VT switches across
> + * suspend/resume, depending on how they handle restoring video state and
> + * what may be running.
> + *
> + * Drivers can indicate support for switchless suspend/resume, which can
> + * save time and flicker, by using this routine and passing 'false' as
> + * the argument.  If any loaded driver needs VT switching, or the
> + * no_console_suspend argument has been passed on the command line, VT
> + * switches will occur.
> + */

It seems to me that we'll need a separate counter for the number of registered
drivers and do the switch if that number is equal to the number of drivers that
have passed false to this thing.

In which case we can simplify this slightly and introduce
pm_vt_swtich_not_required(void) and then the only drivers that need to bother
will be the ones known to not require the switch.

Otherwise it will be kind of error prone I'm afraid.

Thanks,
Rafael


> +void pm_vt_switch_required(bool required)
> +{
> +	spin_lock(&vt_switch_lock);
> +	if (vt_switch_required == -1) {
> +		/* First call, set up real value */
> +		if (!required)
> +			vt_switch_required = 0;
> +		if (required)
> +			vt_switch_required = 1;
> +	} else {
> +		/*
> +		 * Subsequent caller, make sure we handle the case
> +		 * where a driver binds, needs VT switch, but then unbinds
> +		 * later and a switchless driver is present.
> +		 */
> +		if (!required && vt_switch_required > 0)
> +			vt_switch_required--;
> +		else if (required)
> +			vt_switch_required++;
> +	}
> +	spin_unlock(&vt_switch_lock);
> +}
> +EXPORT_SYMBOL(pm_vt_switch_required);
> +
> +static bool pm_vt_switch(void)
> +{
> +	bool ret = true;
> +
> +	spin_lock(&vt_switch_lock);
> +	if (!vt_switch_required && console_suspend_enabled)
> +		ret = false;
> +	spin_unlock(&vt_switch_lock);
> +	return ret;
> +}
> +
>  int pm_prepare_console(void)
>  {
> +	if (!pm_vt_switch())
> +		return 0;
> +
>  	orig_fgconsole = vt_move_to_console(SUSPEND_CONSOLE, 1);
>  	if (orig_fgconsole < 0)
>  		return 1;
> @@ -26,6 +82,9 @@ int pm_prepare_console(void)
>  
>  void pm_restore_console(void)
>  {
> +	if (!pm_vt_switch())
> +		return;
> +
>  	if (orig_fgconsole >= 0) {
>  		vt_move_to_console(orig_fgconsole, 0);
>  		vt_kmsg_redirect(orig_kmsg);
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.