Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Wednesday, May 14, 2014 03:24:21 PM Jacob Pan wrote:
> On Tue, 13 May 2014 03:10:19 +0200
> "Rafael J. Wysocki" <rjw@rjwysocki.net> wrote:
> 
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > 
> > Currently, some subsystems (e.g. PCI and the ACPI PM domain) have to
> > resume all runtime-suspended devices during system suspend, mostly
> > because those devices may need to be reprogrammed due to different
> > wakeup settings for system sleep and for runtime PM.
> > 
> > For some devices, though, it's OK to remain in runtime suspend 
> > throughout a complete system suspend/resume cycle (if the device was
> > in runtime suspend at the start of the cycle).  We would like to do
> > this whenever possible, to avoid the overhead of extra power-up and
> > power-down events.
> > 
> > However, problems may arise because the device's descendants may
> > require it to be at full power at various points during the cycle.
> > Therefore the most straightforward way to do this safely is if the
> > device and all its descendants can remain runtime suspended until the
> > complete stage of system resume.
> > 
> > To this end, introduce a new device PM flag, power.direct_complete
> > and modify the PM core to use that flag as follows.
> > 
> > If the ->prepare() callback of a device returns a positive number,
> > the PM core will regard that as an indication that it may leave the
> > device runtime-suspended.  It will then check if the system power
> > transition in progress is a suspend (and not hibernation in
> > particular) and if the device is, indeed, runtime-suspended.  In that
> > case, the PM core will set the device's power.direct_complete flag.
> > Otherwise it will clear power.direct_complete for the device and it
> > also will later clear it for the device's parent (if there's one).
> > 
> > Next, the PM core will not invoke the ->suspend() ->suspend_late(),
> > ->suspend_irq(), ->resume_irq(), ->resume_early(), or ->resume()
> > callbacks for all devices having power.direct_complete set.  It
> > will invoke their ->complete() callbacks, however, and those
> > callbacks are then responsible for resuming the devices as
> > appropriate, if necessary.
> > 
> > Changelog partly based on an Alan Stern's description of the idea
> > (http://marc.info/?l=linux-pm&m=139940466625569&w=2).
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/base/power/main.c |   45
> > ++++++++++++++++++++++++++++-----------------
> > include/linux/pm.h        |    1 + 2 files changed, 29 insertions(+),
> > 17 deletions(-)
> > 
> > Index: linux-pm/include/linux/pm.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/pm.h
> > +++ linux-pm/include/linux/pm.h
> > @@ -546,6 +546,7 @@ struct dev_pm_info {
> >  	bool			is_late_suspended:1;
> >  	bool			ignore_children:1;
> >  	bool			early_init:1;	/* Owned by
> > the PM core */
> > +	bool			direct_complete:1;	/*
> > Owned by the PM core */ spinlock_t		lock;
> >  #ifdef CONFIG_PM_SLEEP
> >  	struct list_head	entry;
> > Index: linux-pm/drivers/base/power/main.c
> > ===================================================================
> > --- linux-pm.orig/drivers/base/power/main.c
> > +++ linux-pm/drivers/base/power/main.c
> > @@ -479,7 +479,7 @@ static int device_resume_noirq(struct de
> >  	TRACE_DEVICE(dev);
> >  	TRACE_RESUME(0);
> >  
> > -	if (dev->power.syscore)
> > +	if (dev->power.syscore || dev->power.direct_complete)
> >  		goto Out;
> >  
> >  	if (!dev->power.is_noirq_suspended)
> > @@ -605,7 +605,7 @@ static int device_resume_early(struct de
> >  	TRACE_DEVICE(dev);
> >  	TRACE_RESUME(0);
> >  
> > -	if (dev->power.syscore)
> > +	if (dev->power.syscore || dev->power.direct_complete)
> >  		goto Out;
> >  
> >  	if (!dev->power.is_late_suspended)
> > @@ -732,7 +732,7 @@ static int device_resume(struct device *
> >  	TRACE_DEVICE(dev);
> >  	TRACE_RESUME(0);
> >  
> > -	if (dev->power.syscore)
> > +	if (dev->power.syscore || dev->power.direct_complete)
> >  		goto Complete;
> >  
> >  	dpm_wait(dev->parent, async);
> > @@ -1007,7 +1007,7 @@ static int __device_suspend_noirq(struct
> >  		goto Complete;
> >  	}
> >  
> > -	if (dev->power.syscore)
> > +	if (dev->power.syscore || dev->power.direct_complete)
> >  		goto Complete;
> >  
> >  	dpm_wait_for_children(dev, async);
> > @@ -1146,7 +1146,7 @@ static int __device_suspend_late(struct
> >  		goto Complete;
> >  	}
> >  
> > -	if (dev->power.syscore)
> > +	if (dev->power.syscore || dev->power.direct_complete)
> >  		goto Complete;
> >  
> >  	dpm_wait_for_children(dev, async);
> > @@ -1312,7 +1312,7 @@ static int __device_suspend(struct devic
> >  
> >  	dpm_wait_for_children(dev, async);
> >  
> > -	if (async_error || dev->power.syscore)
> > +	if (async_error || dev->power.syscore ||
> > dev->power.direct_complete) goto Complete;
> >  
> >  	dpm_watchdog_set(&wd, dev);
> > @@ -1365,10 +1365,19 @@ static int __device_suspend(struct devic
> >  
> >   End:
> >  	if (!error) {
> > +		struct device *parent = dev->parent;
> > +
> >  		dev->power.is_suspended = true;
> > -		if (dev->power.wakeup_path
> > -		    && dev->parent
> > && !dev->parent->power.ignore_children)
> > -			dev->parent->power.wakeup_path = true;
> > +		if (parent) {
> > +			spin_lock_irq(&parent->power.lock);
> > +
> > +			dev->parent->power.direct_complete = false;
> should we respect ignore_children flag here? not all parent devices
> create children with proper .prepare() function. this allows parents
> override children.
> I am looking at USB, a USB device could have logical children such as
> ep_xx, they don't go through the same subsystem .prepare().

Well, I'm not sure about that.  Let me consider that for a while.

Alan, what do you think?

> 
> > +			if (dev->power.wakeup_path
> > +			    && !dev->parent->power.ignore_children)
> > +				dev->parent->power.wakeup_path =
> > true; +
> > +			spin_unlock_irq(&parent->power.lock);
> > +		}
> >  	}
> >  
> >  	device_unlock(dev);
> > @@ -1470,7 +1479,7 @@ static int device_prepare(struct device
> >  {
> >  	int (*callback)(struct device *) = NULL;
> >  	char *info = NULL;
> > -	int error = 0;
> > +	int ret = 0;
> >  
> >  	if (dev->power.syscore)
> >  		return 0;
> > @@ -1518,17 +1527,19 @@ static int device_prepare(struct device
> >  		callback = dev->driver->pm->prepare;
> >  	}
> >  
> > -	if (callback) {
> > -		error = callback(dev);
> > -		suspend_report_result(callback, error);
> > -	}
> > +	if (callback)
> > +		ret = callback(dev);
> >  
> >  	device_unlock(dev);
> >  
> > -	if (error)
> > +	if (ret < 0) {
> > +		suspend_report_result(callback, ret);
> >  		pm_runtime_put(dev);
> > -
> > -	return error;
> > +		return ret;
> > +	}
> > +	dev->power.direct_complete = ret > 0 && state.event ==
> > PM_EVENT_SUSPEND
> > +					&& pm_runtime_suspended(dev);
> > +	return 0;
> >  }
> >  
> >  /**
> > 
> > --

Rafael