Re: [PATCH] USB: serial: pl2303: account for deficits of clones

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sun, Sep 01, 2024 at 11:11:29PM +0200, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> There are apparently incomplete clones of the HXD type chip in use.
> Those return -EPIPE on GET_LINE_REQUEST and BREAK_REQUEST. Avoid
> flooding the kernel log with those errors. Rather use the
> line_settings cache for GET_LINE_REQUEST and signal missing support by
> returning -ENOTTY from pl2303_set_break.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  drivers/usb/serial/pl2303.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
> index d93f5d584557..04cafa819390 100644
> --- a/drivers/usb/serial/pl2303.c
> +++ b/drivers/usb/serial/pl2303.c
> @@ -731,12 +731,13 @@ static int pl2303_get_line_request(struct usb_serial_port *port,
>  				GET_LINE_REQUEST, GET_LINE_REQUEST_TYPE,
>  				0, 0, buf, 7, 100);
>  	if (ret != 7) {
> -		dev_err(&port->dev, "%s - failed: %d\n", __func__, ret);
> +		struct pl2303_private *priv = usb_get_serial_port_data(port);
>  
> -		if (ret >= 0)
> -			ret = -EIO;
> +		dev_dbg(&port->dev, "%s - failed, falling back on cache: %d\n",
> +			__func__, ret);
> +		memcpy(buf, priv->line_settings, 7);

Ugh, how is this device working in other operating systems?

>  
> -		return ret;
> +		return 0;
>  	}
>  
>  	dev_dbg(&port->dev, "%s - %7ph\n", __func__, buf);
> @@ -1078,8 +1079,8 @@ static int pl2303_set_break(struct usb_serial_port *port, bool enable)
>  				 BREAK_REQUEST, BREAK_REQUEST_TYPE, state,
>  				 0, NULL, 0, 100);
>  	if (result) {
> -		dev_err(&port->dev, "error sending break = %d\n", result);
> -		return result;
> +		dev_dbg(&port->dev, "error sending break = %d\n", result);
> +		return -ENOTTY;

Are you sure that ENOTTY is correct here?  Why not just send back
-EINVAL or something like that telling userspace that this is not
allowed for this device?

thanks,

greg k-h