[bigeasy-staging:arm-locking-v2 3/4] drivers/gpio/gpio-bcm-kona.c:301:12: warning: 'res' may be used uninitialized in this function

[bigeasy-staging:arm-locking-v2 3/4] drivers/gpio/gpio-bcm-kona.c:301:12: warning: 'res' may be used uninitialized in this function

[kbuild test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/staging.git arm-locking-v2
head:   c6339276cd4a34957bd9ba40e0a415c8755b54aa
commit: ee1a9ea5a47977cc72768b6da279635b9d9b858a [3/4] ARM: Inline locking functions for !PREEMPTION
config: arm-multi_v7_defconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout ee1a9ea5a47977cc72768b6da279635b9d9b858a
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=arm 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

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/gpio/gpio-bcm-kona.c: In function 'bcm_kona_gpio_set_config':
>> drivers/gpio/gpio-bcm-kona.c:301:12: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
          (res << GPIO_GPCTR0_DBR_SHIFT);
          ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/gpio/gpio-bcm-kona.c:267:11: note: 'res' was declared here
     u32 val, res;
              ^~~

vim +/res +301 drivers/gpio/gpio-bcm-kona.c

757651e3d60e5b Markus Mayer     2013-09-10  261  
757651e3d60e5b Markus Mayer     2013-09-10  262  static int bcm_kona_gpio_set_debounce(struct gpio_chip *chip, unsigned gpio,
757651e3d60e5b Markus Mayer     2013-09-10  263  				      unsigned debounce)
757651e3d60e5b Markus Mayer     2013-09-10  264  {
757651e3d60e5b Markus Mayer     2013-09-10  265  	struct bcm_kona_gpio *kona_gpio;
757651e3d60e5b Markus Mayer     2013-09-10  266  	void __iomem *reg_base;
757651e3d60e5b Markus Mayer     2013-09-10  267  	u32 val, res;
757651e3d60e5b Markus Mayer     2013-09-10  268  	unsigned long flags;
757651e3d60e5b Markus Mayer     2013-09-10  269  
ba4a74485a32c1 Linus Walleij    2015-12-04  270  	kona_gpio = gpiochip_get_data(chip);
757651e3d60e5b Markus Mayer     2013-09-10  271  	reg_base = kona_gpio->reg_base;
757651e3d60e5b Markus Mayer     2013-09-10  272  	/* debounce must be 1-128ms (or 0) */
757651e3d60e5b Markus Mayer     2013-09-10  273  	if ((debounce > 0 && debounce < 1000) || debounce > 128000) {
58383c78425e4e Linus Walleij    2015-11-04  274  		dev_err(chip->parent, "Debounce value %u not in range\n",
757651e3d60e5b Markus Mayer     2013-09-10  275  			debounce);
757651e3d60e5b Markus Mayer     2013-09-10  276  		return -EINVAL;
757651e3d60e5b Markus Mayer     2013-09-10  277  	}
757651e3d60e5b Markus Mayer     2013-09-10  278  
757651e3d60e5b Markus Mayer     2013-09-10  279  	/* calculate debounce bit value */
757651e3d60e5b Markus Mayer     2013-09-10  280  	if (debounce != 0) {
757651e3d60e5b Markus Mayer     2013-09-10  281  		/* Convert to ms */
757651e3d60e5b Markus Mayer     2013-09-10  282  		debounce /= 1000;
757651e3d60e5b Markus Mayer     2013-09-10  283  		/* find the MSB */
757651e3d60e5b Markus Mayer     2013-09-10  284  		res = fls(debounce) - 1;
757651e3d60e5b Markus Mayer     2013-09-10  285  		/* Check if MSB-1 is set (round up or down) */
757651e3d60e5b Markus Mayer     2013-09-10  286  		if (res > 0 && (debounce & BIT(res - 1)))
757651e3d60e5b Markus Mayer     2013-09-10  287  			res++;
757651e3d60e5b Markus Mayer     2013-09-10  288  	}
757651e3d60e5b Markus Mayer     2013-09-10  289  
757651e3d60e5b Markus Mayer     2013-09-10  290  	/* spin lock for read-modify-write of the GPIO register */
c69fcea57e9d2b Julia Cartwright 2017-03-09  291  	raw_spin_lock_irqsave(&kona_gpio->lock, flags);
757651e3d60e5b Markus Mayer     2013-09-10  292  
757651e3d60e5b Markus Mayer     2013-09-10  293  	val = readl(reg_base + GPIO_CONTROL(gpio));
757651e3d60e5b Markus Mayer     2013-09-10  294  	val &= ~GPIO_GPCTR0_DBR_MASK;
757651e3d60e5b Markus Mayer     2013-09-10  295  
757651e3d60e5b Markus Mayer     2013-09-10  296  	if (debounce == 0) {
757651e3d60e5b Markus Mayer     2013-09-10  297  		/* disable debounce */
757651e3d60e5b Markus Mayer     2013-09-10  298  		val &= ~GPIO_GPCTR0_DB_ENABLE_MASK;
757651e3d60e5b Markus Mayer     2013-09-10  299  	} else {
757651e3d60e5b Markus Mayer     2013-09-10  300  		val |= GPIO_GPCTR0_DB_ENABLE_MASK |
757651e3d60e5b Markus Mayer     2013-09-10 @301  		    (res << GPIO_GPCTR0_DBR_SHIFT);
757651e3d60e5b Markus Mayer     2013-09-10  302  	}
757651e3d60e5b Markus Mayer     2013-09-10  303  
757651e3d60e5b Markus Mayer     2013-09-10  304  	writel(val, reg_base + GPIO_CONTROL(gpio));
757651e3d60e5b Markus Mayer     2013-09-10  305  
c69fcea57e9d2b Julia Cartwright 2017-03-09  306  	raw_spin_unlock_irqrestore(&kona_gpio->lock, flags);
757651e3d60e5b Markus Mayer     2013-09-10  307  
757651e3d60e5b Markus Mayer     2013-09-10  308  	return 0;
757651e3d60e5b Markus Mayer     2013-09-10  309  }
757651e3d60e5b Markus Mayer     2013-09-10  310  

:::::: The code at line 301 was first introduced by commit
:::::: 757651e3d60e5bff705743a301d64035b919fd03 gpio: bcm281xx: Add GPIO driver

:::::: TO: Markus Mayer <mmayer@broadcom.com>
:::::: CC: Linus Walleij <linus.walleij@linaro.org>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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