How to open serial port in linux without changing any pin?

Question

Posix requires changing RTS pin on port opening. I want a way to avoid it.

Answer 1

I have no idea why you'd want to do this, but this can be done pretty easily by modifying the linux kernel driver for your serial console so it doesn't toggle RTS. For example, for the 8250-series driver in drivers/tty/serial/8250/ you could change every write to the MCR register (UART_MCR) to ensure that bit 1 (mask is UART_MCR_RTS) is never set.

Since it's abstracted away in userspace, you're out of luck if you want to do this without modifying the kernel driver.