linux-kernel - Re: drivers/clocksource/timer-pistachio.c:74:22: warning: variable 'overflow' set but not used

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Date:   Sun, 14 Nov 2021 13:29:38 -0800
From:   Drew Fustini <drew@...gleboard.org>
To:     kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: drivers/clocksource/timer-pistachio.c:74:22: warning: variable
 'overflow' set but not used

On Fri, Nov 12, 2021 at 07:05:48AM +0800, kernel test robot wrote:
> Hi Drew,
> 
> FYI, the error/warning still remains.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   debe436e77c72fcee804fb867f275e6d31aa999c
> commit: a47d7ef4550d08fb428ea4c3f1a9c71674212208 clocksource/drivers/pistachio: Fix trivial typo
> date:   7 months ago
> config: mips-randconfig-r012-20210927 (attached as .config)
> compiler: mips-linux-gcc (GCC) 11.2.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a47d7ef4550d08fb428ea4c3f1a9c71674212208
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout a47d7ef4550d08fb428ea4c3f1a9c71674212208
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=mips 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    drivers/clocksource/timer-pistachio.c: In function 'pistachio_clocksource_read_cycles':
> >> drivers/clocksource/timer-pistachio.c:74:22: warning: variable 'overflow' set but not used [-Wunused-but-set-variable]
>       74 |         u32 counter, overflow;
>          |                      ^~~~~~~~
> 
> 
> vim +/overflow +74 drivers/clocksource/timer-pistachio.c
> 
>     69	
>     70	static u64 notrace
>     71	pistachio_clocksource_read_cycles(struct clocksource *cs)
>     72	{
>     73		struct pistachio_clocksource *pcs = to_pistachio_clocksource(cs);
>   > 74		u32 counter, overflow;
>     75		unsigned long flags;
>     76	
>     77		/*
>     78		 * The counter value is only refreshed after the overflow value is read.
>     79		 * And they must be read in strict order, hence raw spin lock added.
>     80		 */
>     81	
>     82		raw_spin_lock_irqsave(&pcs->lock, flags);
>     83		overflow = gpt_readl(pcs->base, TIMER_CURRENT_OVERFLOW_VALUE, 0);

I fail to see how variable 'overflow' set but not used as the return
value of gpt_readl() is unconditionally assigned to 'overflow'.

Am I missing something?

Thanks,
Drew