Handling of automatic flow control in UART drivers

[Johannes Thumshirn <johannes.thumshirn@men.de>]

Hi,

We have problem with automatic flow control (i.e. auto RTS/CTS handshaking) in
our uart driver (men_z135_uart.c). It's probably less a technical but a problem
with me understanding the API.

I active the hardware auto flow control feature on the CRTSCTS flag in my
uart_ops->set_termios() function. But then the RTS flag is set on every call of
the uart_ops->set_mctrl() function, this seems to confuse the hardware. Is there
a way to tell the tty layer that flow control is handled solely by hardware?
I.e. is there a way of telling serial core to leave out the calls to
uart_set_mctrl()/uart_clear_mctrl() in uart_throttle()/uart_unthrottle(), or is
setting UPF_FLOW_HARD and then implementing a dummy port->ops->{un}throttle()
the correct way?

Are there any drivers that use a hardware's automatic flow control feature I can
use as an example? A fast grep on AFE reveals some spots, but I can't really
find a difference to my implementation.

Thanks in advance,
	Johannes