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Date:   Sun, 06 Mar 2022 15:29:17 +0000
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: [PATCH -next] misc: rtsx: fix build for CONFIG_PM not set
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Randy Dunlap <rdunlap@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Wei WANG <wei_wang@realsil.com.cn>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
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Hi Jonathan,

Le dim., mars 6 2022 at 15:12:12 +0000, Jonathan Cameron 
<Jonathan.Cameron@Huawei.com> a ?crit :
> On Sun, 27 Feb 2022 17:56:31 +0000
> Paul Cercueil <paul@crapouillou.net> wrote:
> 
>>  Le dim., f?vr. 27 2022 at 18:51:38 +0100, Arnd Bergmann
>>  <arnd@arndb.de> a ?crit :
>>  > On Sun, Feb 27, 2022 at 6:46 PM Paul Cercueil 
>> <paul@crapouillou.net>
>>  > wrote:
>>  >>  Le dim., f?vr. 27 2022 at 18:30:16 +0100, Arnd Bergmann
>>  >>
>>  >>  There could be a DEFINE_DEV_PM_OPS(), but I don't think that's
>>  >> really
>>  >>  needed - you can very well declare your struct dev_pm_ops 
>> without
>>  >> using
>>  >>  one of these macros. Just make sure to use the 
>> SYSTEM_SLEEP_PM_OPS /
>>  >>  RUNTIME_PM_OPS macros for the callbacks and pm_ptr() for the
>>  >> device.pm
>>  >>  pointer.
>>  >
>>  > Ah, of course, so it comes down to
>>  > s/SET_SYSTEM_SLEEP_PM_OPS/SYSTEM_SLEEP_PM_OPS/ while
>>  > removing all the #ifdef an __maybe_unused annotations. The 
>> pm_ptr()
>>  > in driver.pm makes this slightly more optimized AFAICT, but has no
>>  > effect on behavior, right?
>> 
>>  The use of SYSTEM_SLEEP_PM_OPS makes sure that the callbacks are
>>  dropped if the dev_pm_ops is dead code, and the pm_ptr() must be 
>> used
>>  for the compiler to know that the dev_pm_ops is dead code.
>> 
>>  -Paul
>> 
>> 
> 
> Hi Paul,
> 
> We have one remaining case which is still ugly to do.
> Where both SYSTEM_SLEEP_PM_OPS/RUNTIME_PM_OPS are set and
> the dev_pm_ops structure is exported.
> 
> For that one we still need to expose #ifdef fun in the
> drivers I think.
> 
> Any suggestions on a clean solution for that?

Use the _EXPORT_DEV_PM_OPS() macro?

If you make it call __EXPORT_SYMBOL() (with two underscores instead of 
one) you can specify the namespace as well. All you need then is a nice 
wrapper macro in pm_runtime.h, that can be used in the driver.

Cheers,
-Paul

> Currently I have this...
> 
> #ifdef CONFIG_PM
> const struct dev_pm_ops bmc150_magn_pm_ops = {
> 	SYSTEM_SLEEP_PM_OPS(...)
> 	RUNTIME_PM_OPS(...)
> };
> EXPORT_SYMBOL_NS(bmc150_magn_pm_ops, IIO_BMC150_MAGN);
> #else
> static const __maybe_unused dev_pm_ops bmc150_magn_pm_ops = {
> 	SYSTEM_SLEEP_PM_OPS(...)
> 	RUNTIME_PM_OPS(...)
> };
> #endif
> Not super clean but perhaps we do need
> EXPORT_NS_DEV_PM_OPS
> EXPORT_NS_GPL_DEV_PM_OPS
> and potentially the non namespaced versions.
> 
> Thanks,
> 
> Jonathan