linux-kernel - Re: [PATCH 10/13] cpufreq: powernow-k8: Make use of known set but not used variables

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Date:   Tue, 14 Jul 2020 19:43:48 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Andreas Herrmann <herrmann.der.user@...glemail.com>,
        Dominik Brodowski <linux@...do.de>,
        Pavel Machek <pavel@....cz>,
        Paul Devriendt <paul.devriendt@....com>,
        Mark Langsdorf <mark.langsdorf@....com>
Subject: Re: [PATCH 10/13] cpufreq: powernow-k8: Make use of known set but not
 used variables

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.
>
> Fixes the following W=1 kernel build warning(s):
>
>  drivers/cpufreq/powernow-k8.c: In function ‘pending_bit_stuck’:
>  drivers/cpufreq/powernow-k8.c:89:10: warning: variable ‘hi’ set but not used [-Wunused-but-set-variable]
>  89 | u32 lo, hi;
>  | ^~
>  drivers/cpufreq/powernow-k8.c: In function ‘core_voltage_pre_transition’:
>  drivers/cpufreq/powernow-k8.c:285:14: warning: variable ‘lo’ set but not used [-Wunused-but-set-variable]
>  285 | u32 maxvid, lo, rvomult = 1;
>  | ^~
>
> Cc: Andreas Herrmann <herrmann.der.user@...glemail.com>
> Cc: Dominik Brodowski <linux@...do.de>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Paul Devriendt <paul.devriendt@....com>
> Cc: Mark Langsdorf <mark.langsdorf@....com>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  drivers/cpufreq/powernow-k8.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
> index 3984959eed1d5..b76df81044c4f 100644
> --- a/drivers/cpufreq/powernow-k8.c
> +++ b/drivers/cpufreq/powernow-k8.c
> @@ -89,6 +89,7 @@ static int pending_bit_stuck(void)
>         u32 lo, hi;
>
>         rdmsr(MSR_FIDVID_STATUS, lo, hi);
> +       hi &= hi; /* Silence set but not used warning */

Hmm.

What about using __always_unused for this?

>         return lo & MSR_S_LO_CHANGE_PENDING ? 1 : 0;
>  }
>
> @@ -292,6 +293,7 @@ static int core_voltage_pre_transition(struct powernow_k8_data *data,
>                 rvomult = 2;
>         rvosteps *= rvomult;
>         rdmsr(MSR_FIDVID_STATUS, lo, maxvid);
> +       lo &= lo; /* Silence set but not used warning */
>         maxvid = 0x1f & (maxvid >> 16);
>         pr_debug("ph1 maxvid=0x%x\n", maxvid);
>         if (reqvid < maxvid) /* lower numbers are higher voltages */
> --
> 2.25.1
>