Hi Krzysztof,

First bad commit (maybe != root cause):

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   dd860052c99b1e088352bdd4fb7aef46f8d2ef47
commit: 7a69a6f68da5084e7f42df18bbc3b38f3785cccf mfd: omap-usb: Depend on COMMON_CLK to fix compile tests
date:   5 months ago
config: mips-randconfig-c023-20210508 (attached as .config)
compiler: mipsel-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/torvalds/linux.git/commit/?id=7a69a6f68da5084e7f42df18bbc3b38f3785cccf
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout 7a69a6f68da5084e7f42df18bbc3b38f3785cccf
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross W=1 ARCH=mips 

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

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: "rt_sysc_membase" [drivers/watchdog/rt2880_wdt.ko] undefined!

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