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

From: Drew Fustini
Date: Sun Nov 14 2021 - 16:30:12 EST


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@xxxxxxxxx>
>
> 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