linux-kernel - Re: [PATCH 08/13] cpufreq: acpi-cpufreq: Take 'dummy' principle one stage further

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Message-ID: <20200714210056.GF1398296@dell>
Date:   Tue, 14 Jul 2020 22:00:56 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Denis Sadykov <denis.m.sadykov@...el.com>,
        Andy Grover <andrew.grover@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Diefenbaugh <paul.s.diefenbaugh@...el.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Dominik Brodowski <linux@...do.de>
Subject: Re: [PATCH 08/13] cpufreq: acpi-cpufreq: Take 'dummy' principle one
 stage further

On Tue, 14 Jul 2020, Robin Murphy wrote:

> On 2020-07-14 17:03, Rafael J. Wysocki wrote:
> > On Tue, Jul 14, 2020 at 4:51 PM Lee Jones <lee.jones@...aro.org> wrote:
> > > 
> > > If we fail to use a variable, even a 'dummy' one, then the compiler
> > > complains that it is set but not used.  We know this is fine, so we
> > > set it to its own value here.
> > 
> > Which is kind of ugly in my personal view.  I hope that the compiler
> > will actually optimize the extra code away ...
> > 
> > > Fixes the following W=1 kernel build warning(s):
> > 
> > Well, "Makes the following ... warning(s) go away:" rather ...
> 
> Isn't that what we have __maybe_unused and __always_unused for?

Yes, that would be better.

I didn't know you could do that with standard variables.

Will fix.

> > >   drivers/cpufreq/acpi-cpufreq.c: In function ‘cpu_freq_read_intel’:
> > >   drivers/cpufreq/acpi-cpufreq.c:247:11: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
> > >   drivers/cpufreq/acpi-cpufreq.c: In function ‘cpu_freq_read_amd’:
> > >   drivers/cpufreq/acpi-cpufreq.c:265:11: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
> > > 
> > > Cc: Andy Grover <andrew.grover@...el.com>
> > > Cc: Paul Diefenbaugh <paul.s.diefenbaugh@...el.com>
> > > Cc: Dominik Brodowski <linux@...do.de>
> > > Cc: Denis Sadykov <denis.m.sadykov@...el.com>
> > > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > > ---
> > >   drivers/cpufreq/acpi-cpufreq.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> > > index 429e5a36c08a9..d38a693b48e03 100644
> > > --- a/drivers/cpufreq/acpi-cpufreq.c
> > > +++ b/drivers/cpufreq/acpi-cpufreq.c
> > > @@ -247,6 +247,7 @@ static u32 cpu_freq_read_intel(struct acpi_pct_register *not_used)
> > >          u32 val, dummy;
> > > 
> > >          rdmsr(MSR_IA32_PERF_CTL, val, dummy);
> > > +       dummy &= dummy; /* Silence set but not used warning */
> > >          return val;
> > >   }
> > > 
> > > @@ -264,6 +265,7 @@ static u32 cpu_freq_read_amd(struct acpi_pct_register *not_used)
> > >          u32 val, dummy;
> > > 
> > >          rdmsr(MSR_AMD_PERF_CTL, val, dummy);
> > > +       dummy &= dummy; /* Silence set but not used warning */
> > >          return val;
> > >   }
> > > 
> > 
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> > 

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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