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

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Message-ID: <8b2f7674-9e33-e09c-cf99-84c59edb9779@arm.com>
Date:   Tue, 14 Jul 2020 17:20:54 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Lee Jones <lee.jones@...aro.org>
Cc:     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 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?

Robin.

>>   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;
>>   }
>>
>> --
>> 2.25.1
>>
> 
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