Hi Dmitry,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tty/tty-testing]
[also build test WARNING on usb/usb-testing linus/master v5.6-rc4 next-20200302]
[cannot apply to linux/master]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Dmitry-Safonov/serial-sysrq-Add-MAGIC_SYSRQ_SERIAL_SEQUENCE/20200303-041809
base:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing

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

New smatch warnings:
drivers/tty/serial/serial_core.c:3123 uart_try_toggle_sysrq() warn: unsigned '++port->sysrq_seq' is never less than zero.

Old smatch warnings:
drivers/tty/serial/serial_core.c:298 uart_shutdown() error: we previously assumed 'uport' could be null (see line 294)
drivers/tty/serial/serial_core.c:2741 iomem_base_show() warn: argument 4 to %lX specifier is cast from pointer

vim +3123 drivers/tty/serial/serial_core.c

  3099	
  3100	/**
  3101	 *	uart_try_toggle_sysrq - Enables SysRq from serial line
  3102	 *	@port: uart_port structure where char(s) after BREAK met
  3103	 *	@ch: new character in the sequence after received BREAK
  3104	 *
  3105	 *	Enables magic SysRq when the required sequence is met on port
  3106	 *	(see CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE).
  3107	 *
  3108	 *	Returns false if @ch is out of enabling sequence and should be
  3109	 *	handled some other way, true if @ch was consumed.
  3110	 */
  3111	static bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
  3112	{
  3113		if (ARRAY_SIZE(sysrq_toggle_seq) <= 1)
  3114			return false;
  3115	
  3116		BUILD_BUG_ON(ARRAY_SIZE(sysrq_toggle_seq) >= U8_MAX);
  3117		if (sysrq_toggle_seq[port->sysrq_seq] != ch) {
  3118			port->sysrq_seq = 0;
  3119			return false;
  3120		}
  3121	
  3122		/* Without the last \0 */
> 3123		if (++port->sysrq_seq < (ARRAY_SIZE(sysrq_toggle_seq) - 1)) {
  3124			port->sysrq = jiffies + SYSRQ_TIMEOUT;
  3125			return true;
  3126		}
  3127	
  3128		schedule_work(&sysrq_enable_work);
  3129	
  3130		port->sysrq = 0;
  3131		return true;
  3132	}
  3133	#else
  3134	static inline bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
  3135	{
  3136		return false;
  3137	}
  3138	#endif
  3139	

---
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