Re: [PATCH 3/8] PM: core: Add EXPORT[_GPL]_SIMPLE_DEV_PM_OPS macros

[Paul Cercueil]

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.

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) \