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/a7fc56df5a000d97b1b201a3f8a59218f... 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 a7fc56df5a000d97b1b201a3f8a59218fba1ee49 # 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 >>): sound/core/control_led.c:49:19: warning: no previous prototype for 'snd_ctl_led_controls_by_access' [-Wmissing-prototypes] 49 | struct list_head *snd_ctl_led_controls_by_access(unsigned int access) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 244 | void snd_ctl_led_hello(void) | ^~~~~~~~~~~~~~~~~ vim +/snd_ctl_led_hello +244 sound/core/control_led.c 300372c2ee4ebb Jaroslav Kysela 2021-02-11 237 300372c2ee4ebb Jaroslav Kysela 2021-02-11 238 /** 300372c2ee4ebb Jaroslav Kysela 2021-02-11 239 * snd_ctl_led_hello - kernel module reference helper 300372c2ee4ebb Jaroslav Kysela 2021-02-11 240 * 300372c2ee4ebb Jaroslav Kysela 2021-02-11 241 * Call this helper in the module init function when the control LED 300372c2ee4ebb Jaroslav Kysela 2021-02-11 242 * code should be activated for the given driver. 300372c2ee4ebb Jaroslav Kysela 2021-02-11 243 */ 300372c2ee4ebb Jaroslav Kysela 2021-02-11 @244 void snd_ctl_led_hello(void) 300372c2ee4ebb Jaroslav Kysela 2021-02-11 245 { 300372c2ee4ebb Jaroslav Kysela 2021-02-11 246 } 300372c2ee4ebb Jaroslav Kysela 2021-02-11 247 EXPORT_SYMBOL(snd_ctl_led_hello); 300372c2ee4ebb Jaroslav Kysela 2021-02-11 248 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org