On Fri, Sep 13, 2013 at 05:35:12PM +0200, Paul Chavent wrote:
> Signed-off-by: Paul Chavent <paul.chavent@xxxxxxxx>
> ---
> Documentation/pps/pps.txt | 15 +++++++++++++++
> drivers/usb/serial/generic.c | 9 +++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt
> index d35dcdd..67b9a94 100644
> --- a/Documentation/pps/pps.txt
> +++ b/Documentation/pps/pps.txt
> @@ -66,6 +66,21 @@ In LinuxPPS the PPS sources are simply char devices usually mapped
> into files /dev/pps0, /dev/pps1, etc..
>
>
> +PPS with USB to serial devices
> +------------------------------
> +
> +It is possible to grab the PPS from an USB to serial device. However,
> +you should take into account the latencies and jitter introduced by
> +the USB stack. Users has reported clock instability around +-1ms when
> +synchronized with PPS through USB. This isn't suited for time server
> +synchronisation.
> +
> +If your device doesn't report PPS, you can check that the feature is
> +supported by its driver. Most of the time, you only need to add a call
> +to usb_serial_handle_dcd_change after checking the DCD status (see
> +ch341 and pl2303 examples).
> +
> +
> Coding example
> --------------
>
> diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
> index 1f31e6b..877d6e0 100644
> --- a/drivers/usb/serial/generic.c
> +++ b/drivers/usb/serial/generic.c
> @@ -568,6 +568,15 @@ void usb_serial_handle_dcd_change(struct usb_serial_port *usb_port,
> {
> struct tty_port *port = &usb_port->port;
>
> + if (tty) {
> + struct tty_ldisc *ld = tty_ldisc_ref(tty);
> + if (ld) {
> + if (ld->ops->dcd_change)
> + ld->ops->dcd_change(tty, status);
> + tty_ldisc_deref(ld);
> + }
> + }
> +
> dev_dbg(&usb_port->dev, "%s - status %d\n", __func__, status);
Please add your ldisc handling after the debug statement.
Thanks,
Johan
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