Hi,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on stm32/stm32-next]
[also build test WARNING on usb/usb-testing v5.12-rc7]
[cannot apply to tty/tty-testing next-20210409]
[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/dillon-minfei-gmail-com/serial-stm32-optimize-spin-lock-usage/20210412-123607
base:   https://git.kernel.org/pub/scm/linux/kernel/git/atorgue/stm32.git stm32-next
config: riscv-randconfig-r034-20210412 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 9829f5e6b1bca9b61efc629770d28bb9014dec45)
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
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # https://github.com/0day-ci/linux/commit/a0e81ae10c46f768437d61cd3a3dfd4d1250b375
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review dillon-minfei-gmail-com/serial-stm32-optimize-spin-lock-usage/20210412-123607
        git checkout a0e81ae10c46f768437d61cd3a3dfd4d1250b375
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=riscv 

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/tty/serial/stm32-usart.c:280:39: warning: variable 'flags' is uninitialized when used here [-Wuninitialized]
                   spin_unlock_irqrestore(&port->lock, flags);
                                                       ^~~~~
   drivers/tty/serial/stm32-usart.c:217:24: note: initialize the variable 'flags' to silence this warning
           unsigned long c, flags;
                                 ^
                                  = 0
   1 warning generated.


vim +/flags +280 drivers/tty/serial/stm32-usart.c

   211	
   212	static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
   213	{
   214		struct tty_port *tport = &port->state->port;
   215		struct stm32_port *stm32_port = to_stm32_port(port);
   216		const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
   217		unsigned long c, flags;
   218		u32 sr;
   219		char flag;
   220	
   221		if (irqd_is_wakeup_set(irq_get_irq_data(port->irq)))
   222			pm_wakeup_event(tport->tty->dev, 0);
   223	
   224		while (stm32_usart_pending_rx(port, &sr, &stm32_port->last_res,
   225					      threaded)) {
   226			sr |= USART_SR_DUMMY_RX;
   227			flag = TTY_NORMAL;
   228	
   229			/*
   230			 * Status bits has to be cleared before reading the RDR:
   231			 * In FIFO mode, reading the RDR will pop the next data
   232			 * (if any) along with its status bits into the SR.
   233			 * Not doing so leads to misalignement between RDR and SR,
   234			 * and clear status bits of the next rx data.
   235			 *
   236			 * Clear errors flags for stm32f7 and stm32h7 compatible
   237			 * devices. On stm32f4 compatible devices, the error bit is
   238			 * cleared by the sequence [read SR - read DR].
   239			 */
   240			if ((sr & USART_SR_ERR_MASK) && ofs->icr != UNDEF_REG)
   241				writel_relaxed(sr & USART_SR_ERR_MASK,
   242					       port->membase + ofs->icr);
   243	
   244			c = stm32_usart_get_char(port, &sr, &stm32_port->last_res);
   245			port->icount.rx++;
   246			if (sr & USART_SR_ERR_MASK) {
   247				if (sr & USART_SR_ORE) {
   248					port->icount.overrun++;
   249				} else if (sr & USART_SR_PE) {
   250					port->icount.parity++;
   251				} else if (sr & USART_SR_FE) {
   252					/* Break detection if character is null */
   253					if (!c) {
   254						port->icount.brk++;
   255						if (uart_handle_break(port))
   256							continue;
   257					} else {
   258						port->icount.frame++;
   259					}
   260				}
   261	
   262				sr &= port->read_status_mask;
   263	
   264				if (sr & USART_SR_PE) {
   265					flag = TTY_PARITY;
   266				} else if (sr & USART_SR_FE) {
   267					if (!c)
   268						flag = TTY_BREAK;
   269					else
   270						flag = TTY_FRAME;
   271				}
   272			}
   273	
   274			if (uart_handle_sysrq_char(port, c))
   275				continue;
   276			uart_insert_char(port, sr, USART_SR_ORE, c, flag);
   277		}
   278	
   279		if (threaded)
 > 280			spin_unlock_irqrestore(&port->lock, flags);
   281		else
   282			spin_unlock(&port->lock);
   283	
   284		tty_flip_buffer_push(tport);
   285	
   286		if (threaded)
   287			spin_lock_irqsave(&port->lock, flags);
   288		else
   289			spin_lock(&port->lock);
   290	}
   291	

---
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