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

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Date:   Thu, 29 Oct 2020 18:59:41 +0800
From:   Coiby Xu <coiby.xu@...il.com>
To:     Hans de Goede <hdegoede@...hat.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 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 made a mistake when I thought PM macros like SIMPLE_DEV_PM_OPS
didn't have this issue). What do you think? Btw, It's easy for me to
add CONFIG_PM_SLEEP for those drivers have PM macro but not
CONFIG_PM_SLEEP since I have already written the necessary automation
scripts.

[1] https://lists.linux-foundation.org/pipermail/linux-pm/2011-February/030215.html

>Also s/CONFIG_PM_CONFIG/CONFIG_PM_SLEEP/ in the commit message.
>

Thank you for pointing out the typo. I've written some scripts to
automate the whole process from changing code to submitting patches.
Somehow there is still this issue.

>Regards,
>
>Hans
>
>
>>
>> Signed-off-by: Coiby Xu <coiby.xu@...il.com>
>> ---
>>  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