linux-kernel - Re: [PATCH] ACPI: processor: Fix function defined but not used warning

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Message-ID: <CAJZ5v0jewY9X5rTQmgsgbpjzy=2bzMPTSV60g9kMkXOcKcS_Ng@mail.gmail.com>
Date: Thu, 4 Sep 2025 17:23:42 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Huisong Li <lihuisong@...wei.com>
Cc: rafael@...nel.org, lenb@...nel.org, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linuxarm@...wei.com, 
	jonathan.cameron@...wei.com, zhanjie9@...ilicon.com, zhenglifeng1@...wei.com, 
	yubowen8@...wei.com
Subject: Re: [PATCH] ACPI: processor: Fix function defined but not used warning

On Thu, Sep 4, 2025 at 2:11 PM Huisong Li <lihuisong@...wei.com> wrote:
>
> If CONFIG_ACPI_PROCESSOR=n and CONFIG_ACPI_PROCESSOR_IDLE=n, we may
> encounter some compling warnings as the following link said.
> So remove these empty function definition because they are just used
> in processor_driver.c and if CONFIG_ACPI_PROCESSOR is selected and
> CONFIG_ACPI_PROCESSOR_IDLE also be selected automatically.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202508300519.tZQHY6HA-lkp@intel.com/
>
> Signed-off-by: Huisong Li <lihuisong@...wei.com>
> ---
>  include/acpi/processor.h | 34 +++-------------------------------
>  1 file changed, 3 insertions(+), 31 deletions(-)
>
> diff --git a/include/acpi/processor.h b/include/acpi/processor.h
> index 360b673f05e5..a4e1081fd0da 100644
> --- a/include/acpi/processor.h
> +++ b/include/acpi/processor.h
> @@ -417,40 +417,17 @@ static inline void acpi_processor_throttling_init(void) {}
>  #endif /* CONFIG_ACPI_CPU_FREQ_PSS */
>
>  /* in processor_idle.c */
> -extern struct cpuidle_driver acpi_idle_driver;
>  #ifdef CONFIG_ACPI_PROCESSOR_IDLE
> +extern struct cpuidle_driver acpi_idle_driver;

Are the changes above related to the warning?  If not, maybe move them
to a separate patch?

>  int acpi_processor_power_init(struct acpi_processor *pr);
>  int acpi_processor_power_exit(struct acpi_processor *pr);
>  int acpi_processor_power_state_has_changed(struct acpi_processor *pr);
>  int acpi_processor_hotplug(struct acpi_processor *pr);
>  void acpi_processor_register_idle_driver(void);
>  void acpi_processor_unregister_idle_driver(void);
> -#else
> -static inline int acpi_processor_power_init(struct acpi_processor *pr)
> -{
> -       return -ENODEV;
> -}
> -
> -static inline int acpi_processor_power_exit(struct acpi_processor *pr)
> -{
> -       return -ENODEV;
> -}
> -
> -static inline int acpi_processor_power_state_has_changed(struct acpi_processor *pr)
> -{
> -       return -ENODEV;
> -}
>
> -static inline int acpi_processor_hotplug(struct acpi_processor *pr)
> -{
> -       return -ENODEV;
> -}
> -static inline void acpi_processor_register_idle_driver(void)
> -{
> -}
> -static inline void acpi_processor_unregister_idle_driver(void)
> -{
> -}
> +extern int acpi_processor_ffh_lpi_probe(unsigned int cpu);
> +extern int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi);

Please remove the "extern" from these declarations.

>  #endif /* CONFIG_ACPI_PROCESSOR_IDLE */
>
>  /* in processor_thermal.c */
> @@ -473,11 +450,6 @@ static inline void acpi_thermal_cpufreq_exit(struct cpufreq_policy *policy)
>  }
>  #endif /* CONFIG_CPU_FREQ */
>
> -#ifdef CONFIG_ACPI_PROCESSOR_IDLE
> -extern int acpi_processor_ffh_lpi_probe(unsigned int cpu);
> -extern int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi);
> -#endif
> -
>  void acpi_processor_init_invariance_cppc(void);
>
>  #endif
> --