linux-kernel - Re: [PATCH] USB: serial: f81534: Detect errors from f81534_logic_to_phy

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Date:   Thu, 15 Dec 2016 16:29:30 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Johan Hovold <johan@...nel.org>,
        "Ji-Ze Hong (Peter Hong)" <hpeter@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: f81534: Detect errors from
 f81534_logic_to_phy_port()

On Wed, Dec 14, 2016 at 12:18:53PM +0100, Geert Uytterhoeven wrote:
> With gcc 4.1.2:
> 
>     drivers/usb/serial/f81534.c: In function ‘f81534_port_probe’:
>     drivers/usb/serial/f81534.c:1250: warning: comparison is always false due to limited range of data type
> 
> f81534_logic_to_phy_port() may return a negative error value, which is
> ignored by assigning it to u8 f81534_port_private.phy_num.

Thanks for fixing this.

> Use an intermediate variable of type int to fix this.
> While at it, forward the actual error code instead of converting it to
> -ENODEV.
>
> Fixes: 0c9bd6004d258d46 ("USB: serial: add Fintek F81532/534 driver")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>  drivers/usb/serial/f81534.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
> index 8282a6a18fee83f6..2acad268f9d15f43 100644
> --- a/drivers/usb/serial/f81534.c
> +++ b/drivers/usb/serial/f81534.c
> @@ -1237,6 +1237,7 @@ static int f81534_attach(struct usb_serial *serial)
>  static int f81534_port_probe(struct usb_serial_port *port)
>  {
>  	struct f81534_port_private *port_priv;
> +	int ret;
>  
>  	port_priv = devm_kzalloc(&port->dev, sizeof(*port_priv), GFP_KERNEL);
>  	if (!port_priv)
> @@ -1246,10 +1247,14 @@ static int f81534_port_probe(struct usb_serial_port *port)
>  	mutex_init(&port_priv->mcr_mutex);
>  
>  	/* Assign logic-to-phy mapping */
> -	port_priv->phy_num = f81534_logic_to_phy_port(port->serial, port);
> -	if (port_priv->phy_num < 0 || port_priv->phy_num >= F81534_NUM_PORT)
> +	ret = f81534_logic_to_phy_port(port->serial, port);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ret >= F81534_NUM_PORT)
>  		return -ENODEV;

How about dropping the redundant >= F81534_NUM_PORT test as well as the
helper function will never return anything that large?

>  
> +	port_priv->phy_num = ret;
>  	usb_set_serial_port_data(port, port_priv);
>  	dev_dbg(&port->dev, "%s: port_number: %d, phy_num: %d\n", __func__,
>  			port->port_number, port_priv->phy_num);

Thanks,
Johan