Re: [PATCH] serial: stm32: optimize spin lock usage

[dillon min <dillon.minfei@gmail.com>]

Hi lkp,

Thanks for the reminder.
I just noticed this from greg's mail. still waiting for his response
about the proper solution for this patch.
After that i will update version 2 for it.

Your test is really efficient, thanks.

Best regards,

Dillon.

On Mon, Apr 12, 2021 at 3:25 PM kernel test robot <lkp@intel.com> wrote:
>
> 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
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org