Re: [PATCH v1] cpufreq: CPPC: Fix unused-function warning

[Pierre Gondois]

On 5/30/22 10:20, Viresh Kumar wrote:
> On 30-05-22, 10:12, Pierre Gondois wrote:
> > Building the cppc_cpufreq driver with for arm64 with
> > CONFIG_ENERGY_MODEL=n triggers the following warnings:
> >   drivers/cpufreq/cppc_cpufreq.c:550:12: error: ‘cppc_get_cpu_cost’ defined but not used
> > [-Werror=unused-function]
> >     550 | static int cppc_get_cpu_cost(struct device *cpu_dev, unsigned long KHz,
> >         |            ^~~~~~~~~~~~~~~~~
> >   drivers/cpufreq/cppc_cpufreq.c:481:12: error: ‘cppc_get_cpu_power’ defined but not used
> > [-Werror=unused-function]
> >     481 | static int cppc_get_cpu_power(struct device *cpu_dev,
> >         |            ^~~~~~~~~~~~~~~~~~
> >
> > Fixes: 740fcdc2c20e ("cpufreq: CPPC: Register EM based on efficiency class information")
> > Reported-by: Shaokun Zhang <zhangshaokun@xxxxxxxxxxxxx>
> > Signed-off-by: Pierre Gondois <pierre.gondois@xxxxxxx>
> > ---
> >   drivers/cpufreq/cppc_cpufreq.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> > index d092c9bb4ba3..ecd0d3ee48c5 100644
> > --- a/drivers/cpufreq/cppc_cpufreq.c
> > +++ b/drivers/cpufreq/cppc_cpufreq.c
> > @@ -478,7 +478,7 @@ static inline unsigned long compute_cost(int cpu, int step)
> >   			step * CPPC_EM_COST_STEP;
> >   }
> >   
> > -static int cppc_get_cpu_power(struct device *cpu_dev,
> > +static __maybe_unused int cppc_get_cpu_power(struct device *cpu_dev,
> >   		unsigned long *power, unsigned long *KHz)
> >   {
> >   	unsigned long perf_step, perf_prev, perf, perf_check;
> > @@ -547,8 +547,8 @@ static int cppc_get_cpu_power(struct device *cpu_dev,
> >   	return 0;
> >   }
> >   
> > -static int cppc_get_cpu_cost(struct device *cpu_dev, unsigned long KHz,
> > -		unsigned long *cost)
> > +static __maybe_unused int cppc_get_cpu_cost(struct device *cpu_dev,
> > +		unsigned long KHz, unsigned long *cost)
> >   {
> >   	unsigned long perf_step, perf_prev;
> >   	struct cppc_perf_caps *perf_caps;
>
> Should we actually run cppc_cpufreq_register_em() for
> !CONFIG_ENERGY_MODEL ? Why?

Hello Viresh,
It seems that when CONFIG_ENERGY_MODEL=n, the compiler is already
considering cppc_cpufreq_register_em() as an empty function.

Indeed, CONFIG_ENERGY_MODEL=n makes em_dev_register_perf_domain()
an empty function, so cppc_cpufreq_register_em() is only made of
variable definitions. This compiler optimization also explains
why cppc_get_cpu_power() and cppc_get_cpu_cost() trigger the
-Wunused-function warning.

Putting cppc_cpufreq_register_em() inside an
#ifdef CONFIG_ENERGY_MODEL
guard seems also valid to me. To avoid too many empty definitions
of cppc_cpufreq_register_em(), I guess it should be inside an
#if defined(CONFIG_ARM64) && defined(CONFIG_ENERGY_MODEL)
guard instead.
Please let me know what you prefer.

Regards,
Pierre