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

[Jacob Pan]

On Tue, 13 May 2014 03:10:19 +0200
"Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> 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@xxxxxxxxx>
> ---
>  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().

> +			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;
>  }
>  
>  /**
> 
> --
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[Jacob Pan]
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