[jcmvbkbc-xtensa:xtensa-5.19-esp32 5/9] drivers/tty/serial/esp32_uart.c:33:6: warning: no previous prototype for 'dbg_echo'

[kernel test robot]

tree:   https://github.com/jcmvbkbc/linux-xtensa xtensa-5.19-esp32
head:   a44bcd03203280e59963b3eb3bfba38402be6e33
commit: 88ec52cf55d1fbcbdd78ef3bad5c963b70686883 [5/9] WIP: drivers/tty/serial: add driver for ESP32 UART
config: parisc64-allyesconfig (https://download.01.org/0day-ci/archive/20220611/202206111058.DLtGNJRk-lkp@xxxxxxxxx/config)
compiler: hppa-linux-gcc (GCC) 11.3.0
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://github.com/jcmvbkbc/linux-xtensa/commit/88ec52cf55d1fbcbdd78ef3bad5c963b70686883
        git remote add jcmvbkbc-xtensa https://github.com/jcmvbkbc/linux-xtensa
        git fetch --no-tags jcmvbkbc-xtensa xtensa-5.19-esp32
        git checkout 88ec52cf55d1fbcbdd78ef3bad5c963b70686883
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=parisc SHELL=/bin/bash drivers/dma/ drivers/gpu/drm/mgag200/ drivers/iio/adc/ drivers/regulator/ drivers/tty/serial/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All warnings (new ones prefixed by >>):

>> drivers/tty/serial/esp32_uart.c:33:6: warning: no previous prototype for 'dbg_echo' [-Wmissing-prototypes]
      33 | void dbg_echo(const char *s)
         |      ^~~~~~~~
>> drivers/tty/serial/esp32_uart.c:48:6: warning: no previous prototype for 'dbg_printf' [-Wmissing-prototypes]
      48 | void dbg_printf(const char *fmt, ...)
         |      ^~~~~~~~~~
   drivers/tty/serial/esp32_uart.c: In function 'dbg_printf':
>> drivers/tty/serial/esp32_uart.c:54:9: warning: function 'dbg_printf' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
      54 |         vsnprintf(buf, sizeof(buf), fmt, ap);
         |         ^~~~~~~~~


vim +/dbg_echo +33 drivers/tty/serial/esp32_uart.c

    32	
  > 33	void dbg_echo(const char *s)
    34	{
    35		volatile void __iomem *base = (volatile void __iomem *)0x3ff40000;
    36	
    37		while ((readl(base + UART_STATUS_REG) & UART_TXFIFO_CNT_MASK) != 0)
    38			;
    39	
    40		while (*s) {
    41			if (*s == '\n')
    42				writel('\r', base + UART_FIFO_REG);
    43			writel(*s, base + UART_FIFO_REG);
    44			++s;
    45		}
    46	}
    47	
  > 48	void dbg_printf(const char *fmt, ...)
    49	{
    50		va_list ap;
    51		char buf[256];
    52	
    53		va_start(ap, fmt);
  > 54		vsnprintf(buf, sizeof(buf), fmt, ap);
    55		va_end(ap);
    56		dbg_echo(buf);
    57	}
    58	

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