Hi Jaroslav, I love your patch! Perhaps something to improve: [auto build test WARNING on sound/for-next] [also build test WARNING on v5.11-rc7 next-20210125] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Jaroslav-Kysela/ALSA-control-add... base: https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git for-next config: m68k-allmodconfig (attached as .config) compiler: m68k-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://github.com/0day-ci/linux/commit/050a577337d6c36f0ff05c450d004d776... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Jaroslav-Kysela/ALSA-control-add-generic-LED-trigger-code/20210211-192035 git checkout 050a577337d6c36f0ff05c450d004d7767045f20 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): 78 | struct snd_ctl_led *snd_ctl_led_get_by_access(unsigned int access) | ^~~~~~~~~~~~~~~~~~~~~~~~~ sound/core/control_led.c:271:6: warning: no previous prototype for 'snd_ctl_led_hello' [-Wmissing-prototypes] 271 | void snd_ctl_led_hello(void) | ^~~~~~~~~~~~~~~~~ vim +/snd_ctl_led_get_by_access +78 sound/core/control_led.c 77 79 { 80 unsigned int group = access_to_group(access); 81 if (group >= MAX_LED) 82 return NULL; 83 return &snd_ctl_leds[group]; 84 } 85 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org