linux-kernel - Re: [PATCH] power: supply: olpc_battery: remove unnecessary CONFIG_PM

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Date:   Thu, 29 Oct 2020 12:09:23 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Coiby Xu <coiby.xu@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Darren Hart <dvhart@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Shevchenko <andy@...radead.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 PLATFORM DRIVERS - ARCH" 
        <platform-driver-x86@...r.kernel.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] power: supply: olpc_battery: remove unnecessary
 CONFIG_PM_SLEEP

Hi,

On 10/29/20 11:59 AM, Coiby Xu wrote:
> Hi Hans,
> 
> Thank you for reviewing this patch!
> 
> On Thu, Oct 29, 2020 at 11:04:36AM +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 10/29/20 8:41 AM, Coiby Xu wrote:
>>> SIMPLE_DEV_PM_OPS has already took good care of CONFIG_PM_CONFIG.
>>
>> No it does not, when CONFIG_PM_SLEEP is not set then the
>> SET_SYSTEM_SLEEP_PM_OPS macro which SIMPLE_DEV_PM_OPS uses
>> is a no-op, so nothing will reference xo15_sci_resume leading to
>> a compiler warning when CONFIG_PM_SLEEP is not set.
>>
>> You could drop the ifdef and add __maybe_unused to the definition
>> of xo15_sci_resume, but that feels like needless churn, best to
>> just keep this as is IMHO.
>>
> 
> Actually, this is a tree-wide change by some semi-automation scripts.
> Thank you for pointing out the issue to prevent me from releasing
> another ~150 emails to flood other mailing lists.
> 
> Currently there are 929 drivers has device PM callbacks,
> 
> $ grep -rI "\.pm = &" --include=*.c  ./|wc -l
> 929
> 
> I put all files having device PM callbacks into four categories
> based on weather a file has CONFIG_PM_SLEEP or PM macro like
> SET_SYSTEM_SLEEP_PM_OPS, here are the statistics,
>   1. have both CONFIG_PM_SLEEP and PM_OPS macro: 213
>   2. have CONFIG_PM_SLEEP but no PM_OPS macro: 19
>   3. have PM macro but not CONFIG_PM_SLEEP: 347
>   4. no PM macro or CONFIG_PM_SLEEP: 302
> 
> Some drivers which have PM macro but not CONFIG_PM_SLEEP like
> sound/x86/intel_hdmi_audio.c indeed use __maybe_unused to eliminate
> the compiling warning. In 2011, there's a patch proposing to remove
> ONFIG_PM altogether but an objection was turning CONFIG_PM on would
> increase the kernel size [1]. So __maybe_unused also have this issue.

I would expect the compiler to remove the unused function, it knows
it is unused, that is why __maybe_unused is necessary to suppress
the warning and compilers are pretty smart and agressive wrt remove
unnecessary code these days.

Regards,

Hans




>>> ---
>>>  arch/x86/platform/olpc/olpc-xo15-sci.c | 2 --
>>>  1 file changed, 2 deletions(-)
>>>
>>> diff --git a/arch/x86/platform/olpc/olpc-xo15-sci.c b/arch/x86/platform/olpc/olpc-xo15-sci.c
>>> index 85f4638764d6..716eefd735a4 100644
>>> --- a/arch/x86/platform/olpc/olpc-xo15-sci.c
>>> +++ b/arch/x86/platform/olpc/olpc-xo15-sci.c
>>> @@ -192,7 +192,6 @@ static int xo15_sci_remove(struct acpi_device *device)
>>>      return 0;
>>>  }
>>>
>>> -#ifdef CONFIG_PM_SLEEP
>>>  static int xo15_sci_resume(struct device *dev)
>>>  {
>>>      /* Enable all EC events */
>>> @@ -204,7 +203,6 @@ static int xo15_sci_resume(struct device *dev)
>>>
>>>      return 0;
>>>  }
>>> -#endif
>>>
>>>  static SIMPLE_DEV_PM_OPS(xo15_sci_pm, NULL, xo15_sci_resume);
>>>
>>>
>>
> 
> -- 
> Best regards,
> Coiby
>