On Wed, 5 Jan 2022 10:15:36 +0000
Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
> Hi Jonathan,
>
> Le mer., janv. 5 2022 at 10:03:32 +0000, Jonathan Cameron
> <Jonathan.Cameron@xxxxxxxxxx> a écrit :
> > On Tue, 4 Jan 2022 21:42:09 +0000
> > Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
> >
> >> These macros are defined conditionally, according to CONFIG_PM:
> >> - if CONFIG_PM is enabled, these macros resolve to
> >> DEFINE_SIMPLE_DEV_PM_OPS(), and the dev_pm_ops symbol will be
> >> exported.
> >>
> >> - if CONFIG_PM is disabled, these macros will result in a dummy
> >> static
> >> dev_pm_ops to be created with the __maybe_unused flag. The
> >> dev_pm_ops
> >> will then be discarded by the compiler, along with the provided
> >> callback functions if they are not used anywhere else.
> >>
> >> In the second case, the symbol is not exported, which should be
> >> perfectly fine - users of the symbol should all use the pm_ptr() or
> >> pm_sleep_ptr() macro, so the dev_pm_ops marked as "extern" in the
> >> client's code will never be accessed.
> >>
> >> Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> >> ---
> >> include/linux/pm.h | 33 ++++++++++++++++++++++++++++++---
> >> 1 file changed, 30 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/include/linux/pm.h b/include/linux/pm.h
> >> index 389e600df233..a1ce29566aea 100644
> >> --- a/include/linux/pm.h
> >> +++ b/include/linux/pm.h
> >> @@ -8,6 +8,7 @@
> >> #ifndef _LINUX_PM_H
> >> #define _LINUX_PM_H
> >>
> >> +#include <linux/export.h>
> >> #include <linux/list.h>
> >> #include <linux/workqueue.h>
> >> #include <linux/spinlock.h>
> >> @@ -357,14 +358,40 @@ struct dev_pm_ops {
> >> #define SET_RUNTIME_PM_OPS(suspend_fn, resume_fn, idle_fn)
> >> #endif
> >>
> >> +#define _DEFINE_DEV_PM_OPS(name, \
> >> + suspend_fn, resume_fn, \
> >> + runtime_suspend_fn, runtime_resume_fn, idle_fn) \
> >> +const struct dev_pm_ops name = { \
> >> + SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn) \
> >> + RUNTIME_PM_OPS(runtime_suspend_fn, runtime_resume_fn, idle_fn) \
> >> +}
> >> +
> >
> > one blank line probably enough.
> >
> >> +
> >> /*
> >> * Use this if you want to use the same suspend and resume
> >> callbacks for suspend
> >> * to RAM and hibernation.
> >> */
> >> #define DEFINE_SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> >> -const struct dev_pm_ops name = { \
> >> - SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn) \
> >> -}
> >> + _DEFINE_DEV_PM_OPS(name, suspend_fn, resume_fn, NULL, NULL, NULL)
> >> +
> >> +#ifdef CONFIG_PM
> >> +#define _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn,
> >> runtime_suspend_fn, \
> >> + runtime_resume_fn, idle_fn, sec) \
> >> + _DEFINE_DEV_PM_OPS(name, suspend_fn, resume_fn,
> >> runtime_suspend_fn, \
> >> + runtime_resume_fn, idle_fn); \
> >> + _EXPORT_SYMBOL(name, sec)
> >> +#else
> >> +#define _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn,
> >> runtime_suspend_fn, \
> >> + runtime_resume_fn, idle_fn, sec) \
> >> +static __maybe_unused _DEFINE_DEV_PM_OPS(__static_##name,
> >> suspend_fn, \
> >> + resume_fn, runtime_suspend_fn, \
> >> + runtime_resume_fn, idle_fn)
> >> +#endif
> >> +
> >> +#define EXPORT_SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> >> + _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn, NULL, NULL, NULL,
> >> "")
> >> +#define EXPORT_GPL_SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> >> + _EXPORT_DEV_PM_OPS(name, suspend_fn, resume_fn, NULL, NULL, NULL,
> >> "_gpl")
> >
> > So you can get away with these two cases because the
> > SYSTEM_SLEEP_PM_OPS() all have
> > pm_sleep_ptr() wrappers. However, _EXPORT_DEV_PM_OPS() could be used
> > directly and
> > would require __maybe_unused for the RUNTIME_PM_OPS() parameters
> > which isn't ideal.
>
> I don't see why. On both cases (CONFIG_PM enabled/disabled) the
> runtime-PM callbacks are referenced directly, so at no point do they
> appear as unused; therefore __maybe_unused is not needed.
Ah. I'd miss followed things through. Indeed the 'magic' __static_xxx_pm_ops
structure maintains a reference that the compiler can then remove.
On the plus side, turned out I'd not done a full set of tests with my
own patch set and found one bug in that :)
Acked-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>
> Cheers,
> -Paul
>
> > Maybe I'm missing some reason that isn't a problem though as easy to
> > get lost in
> > these macros. :)
> >
> > You could argue that the _ is meant to indicate that macro shouldn't
> > be used directly
> > but I'm not that optimistic.
> >
> > Jonathan
> >
> >
> >
> >>
> >> /* Deprecated. Use DEFINE_SIMPLE_DEV_PM_OPS() instead. */
> >> #define SIMPLE_DEV_PM_OPS(name, suspend_fn, resume_fn) \
> >
>
>
