On Mon, 6 Jun 2011, Felipe Balbi wrote:
> > But what is the "right thing"? Suppose you want to have conditional
> > support for dev_pm_ops whenever CONFIG_PM is enabled and you _also_
> > want to have conditional support for runtime PM whenever
> > CONFIG_PM_RUNTIME is enabled?
>
> we don't have this today either. Currently everybody does #ifdef
> CONFIG_PM, so either all the data is available, or none is and adding
> another #ifdef CONFIG_PM_RUNTIME for the runtime_* friends, would just
> look even uglier :-)
Like in hcd-pci.c? :-)
> > You can obtain that same guarantee by using #ifdef ... #endif. Even
> > better, you can guarantee that the unused data won't be present at all,
> > as opposed to loaded and then freed.
>
> I agree with you here, but I give you the same question as you gave me.
> How will you have conditional on CONFIG_RUNTIME_PM and CONFIG_PM ? you'd
> need two levels of ifdefs.
Well, you'd need more #ifdefs, no question about that. Whether you
need more _levels_ of #ifdefs is unclear.
> > #ifdef CONFIG_PM
> > #define DEV_PM_OPS_REF(my_pm_ops) &(my_pm_ops)
> > #else
> > #define DEV_PM_OPS_REF(my_pm_ops) NULL
> > #endif
> >
> > Then people could write
> >
> > static struct platform_driver my_driver = {
> > ...
> > .driver = {
> > .pm = DEV_PM_OPS_REF(my_driver_pm_ops),
> > },
> > };
> >
> > without worrying about whether or not my_driver_pm_ops was defined.
> > And only one #ifdef block would be needed.
>
> that'd be nice. Something similar to __exit_p() and __devexit_p()
Right. Maybe even call it __pm_ops_p().
In fact, rather than tying this specifically to dev_pm_ops, it would
make sense to have a general-purpose memory section for code that won't
be used, and an appropriate macro (such as "__unused") to specify that
section attribute. Then the PM core could do:
#ifdef CONFIG_PM
#define __pm_ops
#else
#define __pm_ops __unused
#endif
and that would (I think) put less of a mental burden on people.
> Well, it might work out if pm core makes dev_pm_ops only available on
> CONFIG_PM builds.
Currently the .pm member is part of struct bus_type, struct
device_driver, and others whether CONFIG_PM is enabled or not. I don't
know if removing it when CONFIG_PM is disabled would cause build
problems -- it might.
Alan Stern
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