[linux-stable-rc:linux-4.14.y 8467/9999] arch/mips/loongson64/common/early_printk.c:28:6: warning: no previous prototype for 'prom_putchar'

[linux-stable-rc:linux-4.14.y 8467/9999] arch/mips/loongson64/common/early_printk.c:28:6: warning: no previous prototype for 'prom_putchar'

[kernel test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-4.14.y
head:   e1f7d50ae3a3ec342e87a9b1ce6787bfb8b3c08b
commit: af705a1d0e878fcf90ece79e6f0e9d692dad8349 [8467/9999] MIPS: Disable Loongson MMI instructions for kernel build
config: mips-lemote2f_defconfig (attached as .config)
compiler: mips64el-linux-gcc (GCC) 9.3.0
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://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?id=af705a1d0e878fcf90ece79e6f0e9d692dad8349
        git remote add linux-stable-rc https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
        git fetch --no-tags linux-stable-rc linux-4.14.y
        git checkout af705a1d0e878fcf90ece79e6f0e9d692dad8349
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips 

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

All warnings (new ones prefixed by >>):

   In file included from include/linux/workqueue.h:9,
                    from include/linux/srcu.h:34,
                    from include/linux/notifier.h:16,
                    from include/linux/memory_hotplug.h:7,
                    from include/linux/mmzone.h:782,
                    from include/linux/gfp.h:6,
                    from include/linux/irq.h:18,
                    from arch/mips/include/asm/mach-loongson64/loongson.h:16,
                    from arch/mips/loongson64/common/early_printk.c:14:
   include/linux/timer.h: In function 'timer_setup':
   include/linux/timer.h:179:23: warning: cast between incompatible function types from 'void (*)(struct timer_list *)' to 'void (*)(long unsigned int)' [-Wcast-function-type]
     179 |  __setup_timer(timer, (TIMER_FUNC_TYPE)callback,
         |                       ^
   include/linux/timer.h:144:25: note: in definition of macro '__setup_timer'
     144 |   (_timer)->function = (_fn);    \
         |                         ^~~
   arch/mips/loongson64/common/early_printk.c: At top level:
>> arch/mips/loongson64/common/early_printk.c:28:6: warning: no previous prototype for 'prom_putchar' [-Wmissing-prototypes]
      28 | void prom_putchar(char c)
         |      ^~~~~~~~~~~~


vim +/prom_putchar +28 arch/mips/loongson64/common/early_printk.c

f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  13  
5e983ff654ca3df arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02 @14  #include <loongson.h>
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  15  
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  16  #define PORT(base, offset) (u8 *)(base + offset)
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  17  
db54ff246eae5ac arch/mips/loongson/common/early_printk.c Wu Zhangjin 2009-10-16  18  static inline unsigned int serial_in(unsigned char *base, int offset)
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  19  {
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  20  	return readb(PORT(base, offset));
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  21  }
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  22  
db54ff246eae5ac arch/mips/loongson/common/early_printk.c Wu Zhangjin 2009-10-16  23  static inline void serial_out(unsigned char *base, int offset, int value)
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  24  {
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  25  	writeb(value, PORT(base, offset));
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  26  }
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02  27  
f6a2740d0c1b3fd arch/mips/lemote/lm2e/early_printk.c     Wu Zhangjin 2009-07-02 @28  void prom_putchar(char c)

:::::: The code at line 28 was first introduced by commit
:::::: f6a2740d0c1b3fd0d3cc8ec17e232f82f2d8b14c MIPS: Loongson: Add new early_printk implmentation

:::::: TO: Wu Zhangjin <wuzj@lemote.com>
:::::: CC: Ralf Baechle <ralf@linux-mips.org>

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

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