linux-kernel - Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle subsystems consistently

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Date:	Mon, 14 Feb 2011 11:25:58 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kevin Hilman <khilman@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Len Brown <lenb@...nel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle
 subsystems consistently

On Sat, 12 Feb 2011, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> The code handling system-wide power transitions (eg. suspend-to-RAM)
> can in theory execute callbacks provided by the device's bus type,
> device type and class in each phase of the power transition.  In
> turn, the runtime PM core code only calls one of those callbacks at
> a time, preferring bus type callbacks to device type or class
> callbacks and device type callbacks to class callbacks.
> 
> It seems reasonable to make them both behave in the same way in that
> respect.  Moreover, even though a device may belong to two subsystems
> (eg. bus type and device class) simultaneously, in practice power
> management callbacks for system-wide power transitions are always
> provided by only one of them (ie. if the bus type callbacks are
> defined, the device class ones are not and vice versa).  Thus it is
> possible to modify the code handling system-wide power transitions
> so that it follows the core runtime PM code (ie. treats the
> subsystem callbacks as mutually exclusive).
> 
> On the other hand, the core runtime PM code will choose to execute,
> for example, a runtime suspend callback provided by the device type
> even if the bus type's struct dev_pm_ops object exists, but the
> runtime_suspend pointer in it happens to be NULL.  This is confusing,
> because it may lead to the execution of callbacks from different
> subsystems during different operations (eg. the bus type suspend
> callback may be executed during runtime suspend, while the device
> type callback will be executed during runtime resume).
> 
> Make all of the power management code treat subsystem callbacks in
> a consistent way, such that:
> (1) If the device's bus type is defined (eg. dev->bus is not NULL)
>     and its pm pointer is not NULL, the callbacks from dev->bus->pm
>     will be used.
> (2) If dev->bus is NULL or dev->bus->pm is NULL, but the device's
>     device type is defined (eg. dev->type is not NULL) and its pm
>     pointer is not NULL, the callbacks from dev->type->pm will be
>     used.
> (3) If dev->bus is NULL or dev->bus->pm is NULL and dev->type is
>     NULL or dev->type->pm is NULL, the callbacks from dev->class->pm
>     will be used provided that both dev->class and dev->class->pm
>     are not NULL.

It looks okay, but I haven't tested it.  Just one minor change needed 
in the documentation:

> +All phases use bus, type, or class callbacks (that is, methods defined in
> +dev->bus->pm, dev->type->pm, or dev->class->pm).  These callbacks are mutually
> +exclusive, so if the bus provides a struct dev_pm_ops object pointed to by its
> +pm field (i.e. both dev->bus and dev->bus->pm are defined), the callbacks
> +included in that object (i.e. dev->bus->pm) will be used.  In turn, if the

s/In turn/Otherwise/

> +device type provides a struct dev_pm_ops object pointed to by its pm field
> +(i.e. both dev->type and dev->type->pm are defined), the PM core will used the
> +callbacks from that object (i.e. dev->type->pm).  Finally, if the pm fields of
> +both the bus and device type objects are NULL (or those objects do not exist),
> +the callbacks provided by the class (that is, the callbacks from dev->class->pm)
> +will be used.
>  
>  These callbacks may in turn invoke device- or driver-specific methods stored in
>  dev->driver->pm, but they don't have to.

Alan Stern

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