tree:   https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git mediatek-drm-decouple-sub-driver
head:   01742c252181ef443e1f3fa3cce22e351eaa0c10
commit: 9bc998c4daa0b83fd7c59cc5f5529c3a26bcfd50 [25/27] drm/mediatek: Register vblank callback function
config: arm64-allyesconfig (attached as .config)
compiler: aarch64-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/chunkuang.hu/linux.git/commit/?id=9bc998c4daa0b83fd7c59cc5f5529c3a26bcfd50
        git remote add chunkuang.hu https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git
        git fetch --no-tags chunkuang.hu mediatek-drm-decouple-sub-driver
        git checkout 9bc998c4daa0b83fd7c59cc5f5529c3a26bcfd50
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm64 

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 >>):

>> drivers/gpu/drm/mediatek/mtk_drm_crtc.c:475:6: warning: no previous prototype for 'mtk_crtc_ddp_irq' [-Wmissing-prototypes]
     475 | void mtk_crtc_ddp_irq(void *data)
         |      ^~~~~~~~~~~~~~~~

vim +/mtk_crtc_ddp_irq +475 drivers/gpu/drm/mediatek/mtk_drm_crtc.c

   474	
 > 475	void mtk_crtc_ddp_irq(void *data)
   476	{
   477		struct drm_crtc *crtc = data;
   478		struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
   479		struct mtk_drm_private *priv = crtc->dev->dev_private;
   480	

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