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    SubjectRe: [PATCH 2/3] USB : serial : invoke dcd_change ldisc's handler.
    On Fri, Sep 13, 2013 at 05:35:12PM +0200, Paul Chavent wrote:
    > Signed-off-by: Paul Chavent <paul.chavent@onera.fr>
    > ---
    > 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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