linux-kernel - Re: [PATCH] USB: serial: xr: Add TIOCGRS485 and TIOCSRS485 ioctls

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Date:   Mon, 13 Mar 2023 08:00:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jarkko Sonninen <kasper@....fi>
Cc:     Johan Hovold <johan@...nel.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: xr: Add TIOCGRS485 and TIOCSRS485 ioctls

Nit, your "To:" line was corrupted :(

On Mon, Mar 13, 2023 at 03:04:16AM +0200, Jarkko Sonninen wrote:
> Add support for RS-485 in Exar USB adapters.
> RS-485 mode is controlled by TIOCGRS485 and TIOCSRS485 ioctls.
> Gpio mode register is set to enable RS-485.
> 
> Signed-off-by: Jarkko Sonninen <kasper@....fi>
> ---
>  drivers/usb/serial/xr_serial.c | 72 +++++++++++++++++++++++++++++++++-
>  1 file changed, 71 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
> index fdb0aae546c3..edbb6add087c 100644
> --- a/drivers/usb/serial/xr_serial.c
> +++ b/drivers/usb/serial/xr_serial.c
> @@ -93,6 +93,7 @@ struct xr_txrx_clk_mask {
>  #define XR_GPIO_MODE_SEL_DTR_DSR	0x2
>  #define XR_GPIO_MODE_SEL_RS485		0x3
>  #define XR_GPIO_MODE_SEL_RS485_ADDR	0x4
> +#define XR_GPIO_MODE_RS485_TX_H		0x8
>  #define XR_GPIO_MODE_TX_TOGGLE		0x100
>  #define XR_GPIO_MODE_RX_TOGGLE		0x200
>  
> @@ -237,6 +238,8 @@ static const struct xr_type xr_types[] = {
>  struct xr_data {
>  	const struct xr_type *type;
>  	u8 channel;			/* zero-based index or interface number */
> +	struct serial_rs485 rs485;
> +	spinlock_t lock;
>  };
>  
>  static int xr_set_reg(struct usb_serial_port *port, u8 channel, u16 reg, u16 val)
> @@ -629,6 +632,7 @@ static void xr_set_flow_mode(struct tty_struct *tty,
>  	struct xr_data *data = usb_get_serial_port_data(port);
>  	const struct xr_type *type = data->type;
>  	u16 flow, gpio_mode;
> +	unsigned long flags, rs485_flags;
>  	int ret;
>  
>  	ret = xr_get_reg_uart(port, type->gpio_mode, &gpio_mode);
> @@ -645,9 +649,16 @@ static void xr_set_flow_mode(struct tty_struct *tty,
>  	/* Set GPIO mode for controlling the pins manually by default. */
>  	gpio_mode &= ~XR_GPIO_MODE_SEL_MASK;
>  
> +	spin_lock_irqsave(&data->lock, flags);
> +	rs485_flags = data->rs485.flags;
> +	spin_unlock_irqrestore(&data->lock, flags);
> +	if (rs485_flags & SER_RS485_ENABLED)
> +		gpio_mode |= XR_GPIO_MODE_SEL_RS485 | XR_GPIO_MODE_RS485_TX_H;
> +	else if (C_CRTSCTS(tty) && C_BAUD(tty) != B0)
> +		gpio_mode |= XR_GPIO_MODE_SEL_RTS_CTS;
> +
>  	if (C_CRTSCTS(tty) && C_BAUD(tty) != B0) {
>  		dev_dbg(&port->dev, "Enabling hardware flow ctrl\n");
> -		gpio_mode |= XR_GPIO_MODE_SEL_RTS_CTS;
>  		flow = XR_UART_FLOW_MODE_HW;
>  	} else if (I_IXON(tty)) {
>  		u8 start_char = START_CHAR(tty);
> @@ -827,6 +838,64 @@ static void xr_set_termios(struct tty_struct *tty,
>  	xr_set_flow_mode(tty, port, old_termios);
>  }
>  
> +static int xr_get_rs485_config(struct tty_struct *tty,
> +			 unsigned int __user *argp)
> +{
> +	struct usb_serial_port *port = tty->driver_data;
> +	struct xr_data *data = usb_get_serial_port_data(port);
> +	unsigned long flags;
> +	struct serial_rs485 rs485;
> +
> +	spin_lock_irqsave(&data->lock, flags);
> +	memcpy(&rs485, &data->rs485, sizeof(rs485));

Why are you using the stack for this?  Why not directly access the real
structure instead?  And are you sure you need a lock?  If so, why?

> +	spin_unlock_irqrestore(&data->lock, flags);
> +	dev_dbg(tty->dev, "%s flags %02x\n", __func__, rs485.flags);

dev_dbg() provides __func__ for free, so you never need to provide it
again.  Just use the +f flag when enabling it from userspace.

> +
> +	if (copy_to_user(argp, &rs485, sizeof(rs485)))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +static int xr_set_rs485_config(struct tty_struct *tty,
> +			 unsigned long __user *argp)
> +{
> +	struct usb_serial_port *port = tty->driver_data;
> +	struct xr_data *data = usb_get_serial_port_data(port);
> +	struct serial_rs485 rs485;
> +	unsigned long flags;
> +
> +	if (copy_from_user(&rs485, argp, sizeof(rs485)))
> +		return -EFAULT;
> +
> +	dev_dbg(tty->dev, "%s flags %02x\n", __func__, rs485.flags);

Again, no need for __func__.

> +	rs485.flags &= SER_RS485_ENABLED;
> +	spin_lock_irqsave(&data->lock, flags);
> +	memcpy(&data->rs485, &rs485, sizeof(rs485));
> +	spin_unlock_irqrestore(&data->lock, flags);
> +	xr_set_flow_mode(tty, port, 0);
> +
> +	if (copy_to_user(argp, &data->rs485, sizeof(data->rs485)))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +
> +static int xr_ioctl(struct tty_struct *tty,
> +					unsigned int cmd, unsigned long arg)

Very odd indentation, please fix up.

> +{
> +	void __user *argp = (void __user *)arg;
> +
> +	switch (cmd) {
> +	case TIOCGRS485:
> +		return xr_get_rs485_config(tty, argp);
> +	case TIOCSRS485:
> +		return xr_set_rs485_config(tty, argp);
> +	}
> +	return -ENOIOCTLCMD;

Wrong ioctl return value :(

thanks,

greg k-h