linux-kernel - Re: [PATCH 20/28] mfd: arizona: Remove #ifdef guards for PM related functions

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Date:   Mon, 8 Aug 2022 11:43:31 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Paul Cercueil <paul@...pouillou.net>
CC:     Lee Jones <lee.jones@...aro.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH 20/28] mfd: arizona: Remove #ifdef guards for PM related
 functions

On 08/08/2022 11:06, Paul Cercueil wrote:
> Hi Richard,
> 
> Le lun., août 8 2022 at 10:53:54 +0100, Richard Fitzgerald 
> <rf@...nsource.cirrus.com> a écrit :
>> On 07/08/2022 15:52, Paul Cercueil wrote:
>>> Only export the arizona_pm_ops if CONFIG_PM is set, but leave the
>>> suspend/resume functions (and related code) outside #ifdef guards.
>>>
>>> If CONFIG_PM is not set, the arizona_pm_ops will be defined as
>>> "static __maybe_unused", and the structure plus all the callbacks will
>>> be automatically dropped by the compiler.
>>>
>>> The advantage is then that these functions are now always compiled
>>> independently of any Kconfig option, and thanks to that bugs and
>>> regressions are easier to catch.
>>>
>>> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>> Cc: patches@...nsource.cirrus.com
>>> ---
>>>   drivers/mfd/arizona-core.c | 21 +++++++++++----------
>>>   drivers/mfd/arizona-i2c.c  |  2 +-
>>>   drivers/mfd/arizona-spi.c  |  2 +-
>>>   3 files changed, 13 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/mfd/arizona-core.c b/drivers/mfd/arizona-core.c
>>> index cbf1dd90b70d..c1acc9521f83 100644
>>> --- a/drivers/mfd/arizona-core.c
>>> +++ b/drivers/mfd/arizona-core.c
>>> @@ -480,7 +480,6 @@ static int wm5102_clear_write_sequencer(struct 
>>> arizona *arizona)
>>>       return 0;
>>>   }
>>>   -#ifdef CONFIG_PM
>>>   static int arizona_isolate_dcvdd(struct arizona *arizona)
>>
>> __maybe_unused?
> 
> No need. The symbols are always referenced.
> 
>>>   {
>>>       int ret;
>>> @@ -742,9 +741,7 @@ static int arizona_runtime_suspend(struct device 
>>> *dev)
>>
>> __maybe_unused?
>>
>>>         return 0;
>>>   }
>>> -#endif
>>>   -#ifdef CONFIG_PM_SLEEP
>>>   static int arizona_suspend(struct device *dev)
>>
>> __maybe_unused?
>>
>>>   {
>>>       struct arizona *arizona = dev_get_drvdata(dev);
>>> @@ -784,17 +781,21 @@ static int arizona_resume(struct device *dev)
>>
>> __maybe_unused?
>>
>>>         return 0;
>>>   }
>>> -#endif
>>>   +#ifndef CONFIG_PM
>>> +static __maybe_unused
>>> +#endif
>>
>> No need to ifdef a __maybe_unused.
> 
> Yes, it is needed, because the symbol is conditionally exported. If

Why conditionally export it?

> !CONFIG_PM, we want the compiler to discard the dev_pm_ops
  and all the
> callbacks, hence the "static __maybe_unused". That's the same trick used > in _EXPORT_DEV_PM_OPS().
> 
> (note that this patch is broken as it does not change the struct name, 
> in the !PM case, which causes conflicts with the .h. I'll fix in v2)
> 
>>>   const struct dev_pm_ops arizona_pm_ops = {
>>> -    SET_RUNTIME_PM_OPS(arizona_runtime_suspend,
>>> -               arizona_runtime_resume,
>>> -               NULL)
>>> -    SET_SYSTEM_SLEEP_PM_OPS(arizona_suspend, arizona_resume)
>>> -    SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(arizona_suspend_noirq,
>>> -                      arizona_resume_noirq)
>>> +    RUNTIME_PM_OPS(arizona_runtime_suspend,
>>> +               arizona_runtime_resume,
>>> +               NULL)
>>> +    SYSTEM_SLEEP_PM_OPS(arizona_suspend, arizona_resume)
>>> +    NOIRQ_SYSTEM_SLEEP_PM_OPS(arizona_suspend_noirq,
>>> +                  arizona_resume_noirq)
>>>   };
>>> +#ifdef CONFIG_PM
>>>   EXPORT_SYMBOL_GPL(arizona_pm_ops);
>>> +#endif
>>
>> This ifdeffing is ugly. Why must the structure only be exported if
>> CONFIG_PM is set?
> 
> So that all the PM code is garbage-collected by the compiler if !CONFIG_PM.

The functions will be dropped if they are not referenced. That doesn't
answer why the struct must not be exported.

What is the aim of omitting the struct export?

> 
> Ideally I would use something like EXPORT_SIMPLE_DEV_PM_OPS() which 
> would make the patch much cleaner, but it doesn't support noirq 
> callbacks - and that's why I suggested in the cover letter that maybe a 
> new PM macro can be added if this patch is deemed too messy.
> 
> Cheers,
> -Paul
> 
>>>     #ifdef CONFIG_OF
>>>   static int arizona_of_get_core_pdata(struct arizona *arizona)
>>> diff --git a/drivers/mfd/arizona-i2c.c b/drivers/mfd/arizona-i2c.c
>>> index 6d83e6b9a692..8799d9183bee 100644
>>> --- a/drivers/mfd/arizona-i2c.c
>>> +++ b/drivers/mfd/arizona-i2c.c
>>> @@ -119,7 +119,7 @@ static const struct of_device_id 
>>> arizona_i2c_of_match[] = {
>>>   static struct i2c_driver arizona_i2c_driver = {
>>>       .driver = {
>>>           .name    = "arizona",
>>> -        .pm    = &arizona_pm_ops,
>>> +        .pm    = pm_ptr(&arizona_pm_ops),
>>>           .of_match_table    = of_match_ptr(arizona_i2c_of_match),
>>>       },
>>>       .probe        = arizona_i2c_probe,
>>> diff --git a/drivers/mfd/arizona-spi.c b/drivers/mfd/arizona-spi.c
>>> index 941b0267d09d..da05b966d48c 100644
>>> --- a/drivers/mfd/arizona-spi.c
>>> +++ b/drivers/mfd/arizona-spi.c
>>> @@ -282,7 +282,7 @@ static const struct of_device_id 
>>> arizona_spi_of_match[] = {
>>>   static struct spi_driver arizona_spi_driver = {
>>>       .driver = {
>>>           .name    = "arizona",
>>> -        .pm    = &arizona_pm_ops,
>>> +        .pm    = pm_ptr(&arizona_pm_ops),
>>>           .of_match_table    = of_match_ptr(arizona_spi_of_match),
>>>           .acpi_match_table = ACPI_PTR(arizona_acpi_match),
>>>       },
> 
>