Hi Erwan, FYI, the error/warning still remains. tree: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-4.19.y head: 4707d8e5727387e36ea99c74d5ff0ad227700fd0 commit: 144fdb20e5c8fb4f14a75225ff8de885c78271f5 [7602/9999] serial: stm32: fix word length configuration config: arm-randconfig-r034-20200604 (attached as .config) compiler: arm-linux-gnueabi-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 git checkout 144fdb20e5c8fb4f14a75225ff8de885c78271f5 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm 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 >>, old ones prefixed by <<): drivers/tty/serial/stm32-usart.c: In function 'stm32_transmit_chars_dma': drivers/tty/serial/stm32-usart.c:331:15: warning: variable 'cookie' set but not used [-Wunused-but-set-variable] 331 | dma_cookie_t cookie; | ^~~~~~ drivers/tty/serial/stm32-usart.c: At top level: 602 | unsigned int stm32_get_databits(struct ktermios *termios) | ^~~~~~~~~~~~~~~~~~ drivers/tty/serial/stm32-usart.c: In function 'stm32_of_dma_rx_probe': drivers/tty/serial/stm32-usart.c:930:15: warning: variable 'cookie' set but not used [-Wunused-but-set-variable] 930 | dma_cookie_t cookie; | ^~~~~~ vim +/stm32_get_databits +602 drivers/tty/serial/stm32-usart.c 601 603 { 604 unsigned int bits; 605 606 tcflag_t cflag = termios->c_cflag; 607 608 switch (cflag & CSIZE) { 609 /* 610 * CSIZE settings are not necessarily supported in hardware. 611 * CSIZE unsupported configurations are handled here to set word length 612 * to 8 bits word as default configuration and to print debug message. 613 */ 614 case CS5: 615 bits = 5; 616 break; 617 case CS6: 618 bits = 6; 619 break; 620 case CS7: 621 bits = 7; 622 break; 623 /* default including CS8 */ 624 default: 625 bits = 8; 626 break; 627 } 628 629 return bits; 630 } 631 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org