Hi Jiaxun, FYI, the error/warning still remains. tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master head: 1e2a199f6ccdc15cf111d68d212e2fd4ce65682e commit: b13812ddea615b6507beef24f76540c0c1143c5c MIPS: Loongson2ef: Disable Loongson MMI instructions date: 4 months ago config: mips-randconfig-m031-20210119 (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/torvalds/linux.git/commit... git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git git fetch --no-tags linus master git checkout b13812ddea615b6507beef24f76540c0c1143c5c # 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(a)intel.com&gt; All errors (new ones prefixed by >>): arch/mips/loongson2ef/common/serial.c: In function 'serial_init': 66 | loongson_uart_base; | ^~~~~~~~~~~~~~~~~~ | loongson2_cpu_set_rate arch/mips/loongson2ef/common/serial.c:66:4: note: each undeclared identifier is reported only once for each function it appears in 68 | (void __iomem *)_loongson_uart_base; | ^~~~~~~~~~~~~~~~~~~ vim +66 arch/mips/loongson2ef/common/serial.c 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 57 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 58 static int __init serial_init(void) 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 59 { 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 60 unsigned char iotype; 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 61 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 62 iotype = uart8250_data[mips_machtype].iotype; 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 63 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 64 if (UPIO_MEM == iotype) { 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 65 uart8250_data[mips_machtype].mapbase = 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 @66 loongson_uart_base; 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 67 uart8250_data[mips_machtype].membase = 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 @68 (void __iomem *)_loongson_uart_base; 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 69 } 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 70 else if (UPIO_PORT == iotype) 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 71 uart8250_data[mips_machtype].iobase = 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 72 loongson_uart_base - LOONGSON_PCIIO_BASE; 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 73 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 74 memset(&uart8250_data[mips_machtype + 1], 0, 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 75 sizeof(struct plat_serial8250_port)); 5831fdb099ddeec9 Jiaxun Yang 2019-10-20 76 uart8250_device.dev.platform_data = &uart8250_data[mips_machtype]; 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 77 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 78 return platform_device_register(&uart8250_device); 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 79 } 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 80 module_init(serial_init); 71e2f4dd5a65bd8d Jiaxun Yang 2019-10-20 81 :::::: The code at line 66 was first introduced by commit :::::: 5831fdb099ddeec9849658cd534fdcbb03aa6ff9 MIPS: Loongson2ef: clean up loongson64 related code :::::: TO: Jiaxun Yang <jiaxun.yang(a)flygoat.com&gt; :::::: CC: Paul Burton <paulburton(a)kernel.org&gt; --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org