Re: [RFC][PATCH] Power domains for platform bus type
From: Kevin Hilman
Date: Mon Jan 31 2011 - 17:44:30 EST
Grant Likely <grant.likely@xxxxxxxxxxxx> writes:
> On Mon, Jan 31, 2011 at 11:16:51PM +0100, Rafael J. Wysocki wrote:
>> On Monday, January 31, 2011, Alan Stern wrote:
>> > On Mon, 31 Jan 2011, Rafael J. Wysocki wrote:
>> > > On Monday, January 31, 2011, Alan Stern wrote:
>> > > > On Sun, 30 Jan 2011, Rafael J. Wysocki wrote:
>> > > >
>> > > > > > One thing about this implementation is slightly questionable. The new
>> > > > > > power_domain callbacks were added to the __weak platform PM routines,
>> > > > > > which means they will have to be included in every overriding routine
>> > > > > > provided by a platform imiplementation.
>> > > > > >
>> > > > > > Would it be better to separate these things? Have the power_domain
>> > > > > > callbacks occur in a static outer function which then calls a public
>> > > > > > __weak inner function that can be overridden?
>> > > > >
>> > > > > That certainly is a good idea, but I wasn't sure how to do that. It looks
>> > > > > like I could keep the __weak functions as they are and modify
>> > > > > platform_dev_pm_ops instead to point to a new set of function that in turn
>> > > > > would call the __weak ones. For example, the .suspend pointer in
>> > > > > platform_dev_pm_ops might point to a new function, say
>> > > > > platform_pm_full_suspend() that would call the power domain functions and
>> > > > > the "original" platform_pm_suspend(). Is that what you mean?
>> > > >
>> > > > Yes. But what about the platform_bus_set_pm_ops() interface? Should
>> > > > platform-specific replacements for the pm_ops functions also include
>> > > > the power_domain callbacks?
>> > >
>> > > Well, whoever uses platform_bus_set_pm_ops(), he can simply prevent power
>> > > domains from being used by not defining them in the first place. :-)
>> > But what about the case where the user _does_ want to have power
>> > domains?
>> Ah, OK. The caller of platform_bus_set_pm_ops() will replace the original
>> platform_dev_pm_ops with his own set of operations, so he will not see the
>> power domains.
>> > Do you want to make the replacement routines responsible for
>> > invoking the power-domain callbacks, or should the platform core handle
>> > this automatically?
>> Well, if someone replaces the entire platform_dev_pm_ops object, this means
>> that on his platform power management is substantially different from the
>> generic one. In that case, IMO, he should be responsible for handling all
>> of the subsystem-level aspects of power management, including power domains.
> Part of point of doing something like power_domain is to *get rid* of
> platform_bus_set_pm_ops(). It is a horrid, stop-gap interface that
> doesn't scale. I don't think much consideration needs to be made for
> users of platform_bus_set_pm_ops() in this regard.
As the author of platform_bus_set_pm_ops(), I humbly agree.
Also, the __weak functions here were obsoleted by
platform_bus_set_pm_ops(). Once Magnus moves to
platform_bus_set_pm_ops() (or this new interface) the __weak attributes
should be removed (c.f. commit log below where
platform_bus_set_pm_ops() was added.)
Author: Kevin Hilman <khilman@xxxxxx>
Date: Wed Aug 25 12:50:00 2010 -0700
driver core: platform_bus: allow runtime override of dev_pm_ops
Currently, the platform_bus allows customization of several of the
busses dev_pm_ops methods by using weak symbols so that platform code
can override them. The weak-symbol approach is not scalable when
wanting to support multiple platforms in a single kernel binary.
Instead, provide __init methods for platform code to customize the
dev_pm_ops methods at runtime.
NOTE: after these dynamic methods are merged, the weak symbols should
be removed from drivers/base/platform.c. AFAIK, this will only
affect SH and sh-mobile which should be converted to use this
runtime approach instead of the weak symbols. After SH &
sh-mobile are converted, the weak symobols could be removed.
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