linux-kernel - Re: [PATCH] PM / OPP: optimize dev_pm_opp_set

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Date:	Mon, 25 Jul 2016 14:05:11 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	kbuild test robot <lkp@...el.com>, <vireshk@...nel.org>,
	<nm@...com>, <sboyd@...eaurora.org>, <rjw@...ysocki.net>,
	<gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>
CC:	<kbuild-all@...org>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] PM / OPP: optimize dev_pm_opp_set_rate() a bit

On Mon, 25 Jul 2016 13:19:47 +0800 Jisheng Zhang wrote:

> Dear all,
> 
> On Fri, 22 Jul 2016 22:30:53 +0800 kbuild test robot wrote:
> 
> > Hi,
> > 
> > [auto build test WARNING on pm/linux-next]
> > [also build test WARNING on v4.7-rc7 next-20160722]
> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> > 
> > url:    https://github.com/0day-ci/linux/commits/Jisheng-Zhang/PM-OPP-optimize-dev_pm_opp_set_rate-a-bit/20160722-205339
> > base:   https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
> > config: x86_64-allmodconfig (attached as .config)
> > compiler: gcc-6 (Debian 6.1.1-9) 6.1.1 20160705
> > reproduce:
> >         # save the attached .config to linux build tree
> >         make ARCH=x86_64 
> > 
> > Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> > http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
> > 
> > All warnings (new ones prefixed by >>):
> > 
> >    drivers/base/power/opp/core.c: In function 'dev_pm_opp_set_rate':  
> > >> drivers/base/power/opp/core.c:666:3: warning: 'ou_volt_max' may be used uninitialized in this function [-Wmaybe-uninitialized]    
> >       _set_opp_voltage(dev, reg, ou_volt, ou_volt_min, ou_volt_max);
> >       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
> > >> drivers/base/power/opp/core.c:666:3: warning: 'ou_volt_min' may be used uninitialized in this function [-Wmaybe-uninitialized]
> > >> drivers/base/power/opp/core.c:666:3: warning: 'ou_volt' may be used uninitialized in this function [-Wmaybe-uninitialized]    
> 
> These warnings seem weired. We only use them when !IS_ERR(old_opp), and we
> should already set them if !IS_ERR(old_opp). Another weired thing is if
> we add something, printk e.g in _find_freq_ceil(), then these warnings disappear

Hmm, it looks that gcc will inline _find_freq_ceil(), then gcc can't
detect that ou_volt* are already set. Mark _find_freq_ceil() noinline would fix
the warnings

Thanks,
Jisheng

> 
> Could you please kindly give some suggestions about how to fix these warnings?
>