Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757592Ab3IMPmE (ORCPT ); Fri, 13 Sep 2013 11:42:04 -0400 Received: from briaree.onecert.fr ([134.212.190.4]:37402 "EHLO briaree.onecert.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757519Ab3IMPlo (ORCPT ); Fri, 13 Sep 2013 11:41:44 -0400 From: Paul Chavent To: linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, jhovold@gmail.com, fschaefer.oss@googlemail.com, jslaby@suse.cz, max@suse.de, giometti@enneenne.com Cc: linux-kernel@vger.kernel.org, Paul Chavent Subject: [PATCH 2/3] USB : serial : invoke dcd_change ldisc's handler. Date: Fri, 13 Sep 2013 17:35:12 +0200 Message-Id: <1379086513-2434-3-git-send-email-paul.chavent@onera.fr> X-Mailer: git-send-email 1.7.12.1 In-Reply-To: <1379086513-2434-1-git-send-email-paul.chavent@onera.fr> References: <1379086513-2434-1-git-send-email-paul.chavent@onera.fr> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (briaree.onecert.fr [134.212.190.4]); Fri, 13 Sep 2013 17:41:32 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1949 Lines: 60 Signed-off-by: Paul Chavent --- 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); if (status) -- 1.7.12.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/