On Mon, Nov 20, 2023 at 04:10:55PM +0100, Rasmus Villemoes wrote:
> Add code for handling a rs485-mux-gpio specified in device tree.
Hm, that's a bit terse as a commit message.
> @@ -1457,6 +1466,14 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
> return ret;
> uart_sanitize_serial_rs485(port, &rs485);
> uart_set_rs485_termination(port, &rs485);
> + /*
> + * To avoid glitches on the transmit enable pin, the mux must
> + * be set before calling the driver's ->rs485_config when
> + * disabling rs485 mode, but after when enabling rs485
> + * mode.
> + */
> + if (!(rs485.flags & SER_RS485_ENABLED))
> + uart_set_rs485_mux(port, &rs485);
Can it happen that the UART's FIFO contains characters such that
suddenly switching the mux causes some of them to appear on the
RS-485 transceiver and some on the RS-232 driver?
Shouldn't we wait for the FIFO to drain before making the switch?
I think that would be closer to the behavior expected by user space.
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -584,6 +584,7 @@ struct uart_port {
> struct serial_rs485 rs485_supported; /* Supported mask for serial_rs485 */
> struct gpio_desc *rs485_term_gpio; /* enable RS485 bus termination */
> struct gpio_desc *rs485_rx_during_tx_gpio; /* Output GPIO that sets the state of RS485 RX during TX */
> + struct gpio_desc *rs485_mux_gpio; /* gpio for selecting RS485 mode */
Again, the code comment isn't really helpful as it doesn't add a whole
lot of information to the variable name "rs485_mux_gpio". How about:
"select between RS-232 and RS-485 transceiver" ?
(I realize I made a typo in my previous e-mail about the DT-binding,
sorry about that: s/connect/connected/)
Thanks,
Lukas
