dt-bindings: serial: 8250: Add rate limit for serial port input overruns

When a serial port continuously experiences input overrun from
(1) continuous receive characters from remote and or (2) hardware
issues, its interrupt handler can preempt other tasks especially
when the system is busy (ie. boot up period). This can cause other
tasks to get starved of processing time from the CPU.

When this dts binding is enabled and input overrun on the serial port
is detected, serial port receive will be throttled to give some breathing
room for processing other tasks. Value provided will be in milliseconds.

&serial0{
overrun-throttle-ms = <500>;
};

Signed-off-by: Darwin Dingel <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/8250.txt

···
 - tx-threshold: Specify the TX FIFO low water indication for parts with
   programmable TX FIFO thresholds.
 - resets : phandle + reset specifier pairs
+- overrun-throttle-ms : how long to pause uart rx when input overrun is encountered.
 
 Note:
 * fsl,ns16550: