Re: [PATCH v1 3/4] usb: serial: mxuport: support serial interface mode configuration

[Johan Hovold <johan@kernel.org>]

On Tue, Mar 24, 2026 at 11:50:40AM +0800, Crescent Hsieh wrote:
> Add support for configuring the serial interface mode through
> TIOCSRS485 and TIOCGRS485 using struct serial_rs485.
> 
> Sanitize the requested RS-485 settings and map them to the device
> interface modes before issuing the vendor command to the firmware.
> 
> This allows userspace to switch between RS232, RS422, 2-wire RS485,
> and 4-wire RS485, and to query the current per-port configuration.
> 
> Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
 
> +static void mxuport_sanitize_serial_rs485(struct serial_rs485 *rs485)
> +{
> +	if (!(rs485->flags & SER_RS485_ENABLED)) {
> +		memset(rs485, 0, sizeof(*rs485));
> +		return;
> +	}
> +	if (rs485->flags & SER_RS485_MODE_RS422) {
> +		rs485->flags &= (SER_RS485_ENABLED | SER_RS485_MODE_RS422);
> +		return;
> +	}
> +	rs485->flags &= (SER_RS485_ENABLED | SER_RS485_RX_DURING_TX);

I think you need to clear the other unsupported fields as well (i.e. the
delays).

> +
> +	memset(rs485->padding, 0, sizeof(rs485->padding));
> +}
> +
> +static int mxuport_rs485_config(struct usb_serial_port *port,
> +				struct serial_rs485 *rs485)
> +{
> +	struct usb_serial *serial = port->serial;
> +	u16 mode = MX_INT_RS232;
> +
> +	if (rs485->flags & SER_RS485_ENABLED) {
> +		if (rs485->flags & SER_RS485_MODE_RS422)
> +			mode = MX_INT_RS422;
> +		else if (rs485->flags & SER_RS485_RX_DURING_TX)
> +			mode = MX_INT_4W_RS485;
> +		else
> +			mode = MX_INT_2W_RS485;
> +	}
> +
> +	return mxuport_send_ctrl_urb(serial, RQ_VENDOR_SET_INTERFACE, mode,
> +				     port->port_number);
> +}
> +
> +static int mxuport_get_rs485_config(struct usb_serial_port *port,
> +				    struct serial_rs485 __user *rs485)
> +{
> +	struct mxuport_port *mxport = usb_get_serial_port_data(port);
> +
> +	if (copy_to_user(rs485, &mxport->rs485, sizeof(mxport->rs485)))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +static int mxuport_set_rs485_config(struct usb_serial_port *port,
> +				    struct serial_rs485 __user *rs485_user)
> +{
> +	struct mxuport_port *mxport = usb_get_serial_port_data(port);
> +	struct serial_rs485 rs485;
> +	int ret;
> +
> +	if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
> +		return -EFAULT;
> +
> +	mxuport_sanitize_serial_rs485(&rs485);
> +
> +	ret = mxuport_rs485_config(port, &rs485);
> +	if (!ret)
> +		mxport->rs485 = rs485;

We need some locking here as these ioctls can execute in parallel. 

> +
> +	if (copy_to_user(rs485_user, &mxport->rs485, sizeof(mxport->rs485)))
> +		return -EFAULT;
> +
> +	return 0;
> +}

Johan