Re: [PATCH 3/8] gpio: pci-idio-16: Implement get_multiple callback

[kbuild test robot]

Hi William,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.16-rc5 next-20180313]
[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/William-Breathitt-Gray/Implement-get_multiple-for-ACCES-and-PC104-drivers/20180313-202244
config: x86_64-randconfig-x015-201810 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
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//gpio/gpio-pci-idio-16.c: In function 'idio_16_gpio_get_multiple':
>> drivers//gpio/gpio-pci-idio-16.c:147:35: warning: 'port_state' may be used uninitialized in this function [-Wmaybe-uninitialized]
      bits[BIT_WORD(i)] |= port_state << bit_word_offset;
                           ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~

vim +/port_state +147 drivers//gpio/gpio-pci-idio-16.c

   105	
   106	static int idio_16_gpio_get_multiple(struct gpio_chip *chip,
   107		unsigned long *mask, unsigned long *bits)
   108	{
   109		struct idio_16_gpio *const idio16gpio = gpiochip_get_data(chip);
   110		unsigned int i;
   111		const unsigned int gpio_reg_size = 8;
   112		unsigned int bit_word_offset;
   113		unsigned int bits_mask;
   114		const unsigned long reg_mask = GENMASK(gpio_reg_size, 0);
   115		unsigned long port_state;
   116	
   117		/* clear bits array to a clean slate */
   118		for (i = 0; i < chip->ngpio; i += BITS_PER_LONG)
   119			bits[i / BITS_PER_LONG] = 0;
   120	
   121		/* get bits are evaluated a gpio register size at a time */
   122		for (i = 0; i < chip->ngpio; i += gpio_reg_size) {
   123			bit_word_offset = i % BITS_PER_LONG;
   124			bits_mask = mask[BIT_WORD(i)] & (reg_mask << bit_word_offset);
   125			if (!bits_mask) {
   126				/* no get bits in this register so skip to next one */
   127				continue;
   128			}
   129	
   130			/* read bits from current gpio register */
   131			switch (i / gpio_reg_size) {
   132			case 0:
   133				port_state = ioread8(&idio16gpio->reg->out0_7);
   134				break;
   135			case 1:
   136				port_state = ioread8(&idio16gpio->reg->out8_15);
   137				break;
   138			case 2:
   139				port_state = ioread8(&idio16gpio->reg->in0_7);
   140				break;
   141			case 3:
   142				port_state = ioread8(&idio16gpio->reg->in8_15);
   143				break;
   144			}
   145	
   146			/* store acquired bits */
 > 147			bits[BIT_WORD(i)] |= port_state << bit_word_offset;
   148		}
   149	
   150		return 0;
   151	}
   152	

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