Re: [PATCH V1 2/2] usb:serial: Implement Fintek f81534 break on/off

[Johan Hovold <johan@kernel.org>]

On Fri, Dec 09, 2016 at 01:39:34PM +0800, Ji-Ze Hong (Peter Hong) wrote:
> Implement Fintek f81534 break on/off with LCR register
> It's the same with 16550A LCR register layout
> 
> We'll add a shadow LCR variable to save the final LCR we
> had set due to the "read ep0" operations maybe slow down all
> the serial ports performance.
> 
> Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
> ---
>  drivers/usb/serial/f81534.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
> index 8282a6a..1b6ba81 100644
> --- a/drivers/usb/serial/f81534.c
> +++ b/drivers/usb/serial/f81534.c
> @@ -126,8 +126,10 @@ struct f81534_serial_private {
>  
>  struct f81534_port_private {
>  	struct mutex mcr_mutex;
> +	struct mutex lcr_mutex;

Using a single mutex is preferred.

>  	unsigned long tx_empty;
>  	spinlock_t msr_lock;
> +	u8 shadow_lcr;
>  	u8 shadow_mcr;
>  	u8 shadow_msr;
>  	u8 phy_num;
> @@ -683,6 +685,7 @@ static void f81534_set_termios(struct tty_struct *tty,
>  				struct usb_serial_port *port,
>  				struct ktermios *old_termios)
>  {
> +	struct f81534_port_private *port_priv = usb_get_serial_port_data(port);
>  	u8 new_lcr = 0;
>  	int status;
>  	u32 baud;
> @@ -721,6 +724,10 @@ static void f81534_set_termios(struct tty_struct *tty,
>  		break;
>  	}
>  
> +	mutex_lock(&port_priv->lcr_mutex);
> +	port_priv->shadow_lcr = new_lcr;
> +	mutex_unlock(&port_priv->lcr_mutex);

And this is not sufficient to prevent races with break_ctl. Hold the
mutex while updating LCR in set_port_config at least (and honour the
break state).

> +
>  	baud = tty_get_baud_rate(tty);
>  	if (!baud)
>  		return;
> @@ -812,6 +819,35 @@ static int f81534_read_msr(struct usb_serial_port *port)
>  	return 0;
>  }
>  
> +static void f81534_set_break(struct usb_serial_port *port, bool enable)
> +{
> +	struct f81534_port_private *port_priv = usb_get_serial_port_data(port);
> +	int status;
> +
> +	mutex_lock(&port_priv->lcr_mutex);
> +
> +	if (enable)
> +		port_priv->shadow_lcr |= UART_LCR_SBC;
> +	else
> +		port_priv->shadow_lcr &= ~UART_LCR_SBC;
> +
> +	status = f81534_set_port_register(port, F81534_LINE_CONTROL_REG,
> +			port_priv->shadow_lcr);
> +	if (status) {
> +		dev_err(&port->dev, "%s: set break failed: %x\n", __func__,
> +				status);

%d, __func__ not needed.

> +	}
> +
> +	mutex_unlock(&port_priv->lcr_mutex);
> +}
> +
> +static void f81534_break_ctl(struct tty_struct *tty, int break_state)
> +{
> +	struct usb_serial_port *port = tty->driver_data;
> +
> +	f81534_set_break(port, break_state);
> +}
> +
>  static int f81534_open(struct tty_struct *tty, struct usb_serial_port *port)
>  {
>  	struct f81534_serial_private *serial_priv =
> @@ -877,6 +913,8 @@ static void f81534_close(struct usb_serial_port *port)
>  	}
>  
>  	mutex_unlock(&serial_priv->urb_mutex);
> +
> +	f81534_set_break(port, false);

Drop this too, and fold set_break into break_ctl above.

>  }
>  
>  static int f81534_get_serial_info(struct usb_serial_port *port,
> @@ -1244,6 +1282,7 @@ static int f81534_port_probe(struct usb_serial_port *port)
>  
>  	spin_lock_init(&port_priv->msr_lock);
>  	mutex_init(&port_priv->mcr_mutex);
> +	mutex_init(&port_priv->lcr_mutex);
>  
>  	/* Assign logic-to-phy mapping */
>  	port_priv->phy_num = f81534_logic_to_phy_port(port->serial, port);
> @@ -1389,6 +1428,7 @@ static int f81534_resume(struct usb_serial *serial)
>  	.dtr_rts =		f81534_dtr_rts,
>  	.process_read_urb =	f81534_process_read_urb,
>  	.ioctl =		f81534_ioctl,
> +	.break_ctl =		f81534_break_ctl,
>  	.tiocmget =		f81534_tiocmget,
>  	.tiocmset =		f81534_tiocmset,
>  	.write_bulk_callback =	f81534_write_usb_callback,

Thanks,
Johan