tree:   git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   55f21306900abf9f9d2a087a127ff49c6d388ad2
commit: 7bb72683b1708c3cf3bea0575c0e80314a2232dc [7267/7446] rtc: bq32000: add trickle charger option, with device tree binding
config: i386-randconfig-ib0-09231629 (attached as .config)
reproduce:
  git checkout 7bb72683b1708c3cf3bea0575c0e80314a2232dc
  # save the attached .config to linux build tree
  make ARCH=i386 

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:

   drivers/rtc/rtc-bq32k.c: In function 'trickle_charger_of_init':
   drivers/rtc/rtc-bq32k.c:155:7: warning: assignment makes pointer from integer without a cast
      reg = 0x05;
          ^
   drivers/rtc/rtc-bq32k.c:165:7: warning: assignment makes pointer from integer without a cast
      reg = 0x25;
          ^
   drivers/rtc/rtc-bq32k.c:177:6: warning: assignment makes pointer from integer without a cast
     reg = 0x20;
         ^
   drivers/rtc/rtc-bq32k.c:135:6: warning: unused variable 'plen' [-Wunused-variable]
     int plen = 0;
         ^
   drivers/rtc/rtc-bq32k.c: In function 'bq32k_probe':
>> drivers/rtc/rtc-bq32k.c:169:3: warning: 'setup' may be used uninitialized in this function [-Wmaybe-uninitialized]
      dev_err(dev, "invalid resistor value (%d)\n", *setup);
      ^
   drivers/rtc/rtc-bq32k.c:136:18: note: 'setup' was declared here
     const uint32_t *setup;
                     ^

vim +/setup +169 drivers/rtc/rtc-bq32k.c

   163				return -EINVAL;
   164			}
   165			reg = 0x25;
   166			break;
   167	
   168		default:
   169			dev_err(dev, "invalid resistor value (%d)\n", *setup);
   170			return -EINVAL;
   171		}
   172	
   173		error = bq32k_write(dev, &reg, BQ32K_CFG2, 1);
   174		if (error)
   175			return error;
   176	
   177		reg = 0x20;
   178		error = bq32k_write(dev, &reg, BQ32K_TCH2, 1);
   179		if (error)
   180			return error;

---
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