pps: serial clients support

Adds support, by using the PPS line discipline, for the PPS sources
connected with the CD (Carrier Detect) pin of a serial port.

[akpm@linux-foundation.org: fix cast size warnings]
Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg KH <greg@kroah.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 172 insertions, 1 deletions

diff --git a/drivers/pps/clients/Kconfig b/drivers/pps/clients/Kconfig
index 43ccd3b644f0..4e801bd7254f 100644
--- a/drivers/pps/clients/Kconfig
+++ b/drivers/pps/clients/Kconfig
@@ -15,4 +15,11 @@ config PPS_CLIENT_KTIMER
           This driver can also be built as a module.  If so, the module
           will be called pps-ktimer.
 
+config PPS_CLIENT_LDISC
+        tristate "PPS line discipline"
+        depends on PPS
+        help
+          If you say yes here you get support for a PPS source connected
+          with the CD (Carrier Detect) pin of your serial port.
+
 endif
diff --git a/drivers/pps/clients/Makefile b/drivers/pps/clients/Makefile
index 115572ae3e99..812c9b19b430 100644
--- a/drivers/pps/clients/Makefile
+++ b/drivers/pps/clients/Makefile
@@ -3,6 +3,7 @@
 #
 
 obj-$(CONFIG_PPS_CLIENT_KTIMER) += pps-ktimer.o
+obj-$(CONFIG_PPS_CLIENT_LDISC)  += pps-ldisc.o
 
 ifeq ($(CONFIG_PPS_DEBUG),y)
 EXTRA_CFLAGS += -DDEBUG
diff --git a/drivers/pps/clients/pps-ldisc.c b/drivers/pps/clients/pps-ldisc.c
new file mode 100644
index 000000000000..8e1932d29fd4
--- /dev/null
+++ b/drivers/pps/clients/pps-ldisc.c
@@ -0,0 +1,154 @@
+/*
+ * pps-ldisc.c -- PPS line discipline
+ *
+ *
+ * Copyright (C) 2008   Rodolfo Giometti <giometti@linux.it>
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <linux/module.h>
+#include <linux/serial_core.h>
+#include <linux/tty.h>
+#include <linux/pps_kernel.h>
+
+#define PPS_TTY_MAGIC           0x0001
+
+static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status,
+                                struct timespec *ts)
+{
+        int id = (long)tty->disc_data;
+        struct timespec __ts;
+        struct pps_ktime pps_ts;
+
+        /* First of all we get the time stamp... */
+        getnstimeofday(&__ts);
+
+        /* Does caller give us a timestamp? */
+        if (ts) {       /* Yes. Let's use it! */
+                pps_ts.sec = ts->tv_sec;
+                pps_ts.nsec = ts->tv_nsec;
+        } else {        /* No. Do it ourself! */
+                pps_ts.sec = __ts.tv_sec;
+                pps_ts.nsec = __ts.tv_nsec;
+        }
+
+        /* Now do the PPS event report */
+        pps_event(id, &pps_ts, status ? PPS_CAPTUREASSERT : PPS_CAPTURECLEAR,
+                        NULL);
+
+        pr_debug("PPS %s at %lu on source #%d\n",
+                        status ? "assert" : "clear", jiffies, id);
+}
+
+static int (*alias_n_tty_open)(struct tty_struct *tty);
+
+static int pps_tty_open(struct tty_struct *tty)
+{
+        struct pps_source_info info;
+        struct tty_driver *drv = tty->driver;
+        int index = tty->index + drv->name_base;
+        int ret;
+
+        info.owner = THIS_MODULE;
+        info.dev = NULL;
+        snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
+        snprintf(info.path, PPS_MAX_NAME_LEN, "/dev/%s%d", drv->name, index);
+        info.mode = PPS_CAPTUREBOTH | \
+                        PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
+                        PPS_CANWAIT | PPS_TSFMT_TSPEC;
+
+        ret = pps_register_source(&info, PPS_CAPTUREBOTH | \
+                                PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
+        if (ret < 0) {
+                pr_err("cannot register PPS source \"%s\"\n", info.path);
+                return ret;
+        }
+        tty->disc_data = (void *)(long)ret;
+
+        /* Should open N_TTY ldisc too */
+        ret = alias_n_tty_open(tty);
+        if (ret < 0)
+                pps_unregister_source((long)tty->disc_data);
+
+        pr_info("PPS source #%d \"%s\" added\n", ret, info.path);
+
+        return 0;
+}
+
+static void (*alias_n_tty_close)(struct tty_struct *tty);
+
+static void pps_tty_close(struct tty_struct *tty)
+{
+        int id = (long)tty->disc_data;
+
+        pps_unregister_source(id);
+        alias_n_tty_close(tty);
+
+        pr_info("PPS source #%d removed\n", id);
+}
+
+static struct tty_ldisc_ops pps_ldisc_ops;
+
+/*
+ * Module stuff
+ */
+
+static int __init pps_tty_init(void)
+{
+        int err;
+
+        /* Inherit the N_TTY's ops */
+        n_tty_inherit_ops(&pps_ldisc_ops);
+
+        /* Save N_TTY's open()/close() methods */
+        alias_n_tty_open = pps_ldisc_ops.open;
+        alias_n_tty_close = pps_ldisc_ops.close;
+
+        /* Init PPS_TTY data */
+        pps_ldisc_ops.owner = THIS_MODULE;
+        pps_ldisc_ops.magic = PPS_TTY_MAGIC;
+        pps_ldisc_ops.name = "pps_tty";
+        pps_ldisc_ops.dcd_change = pps_tty_dcd_change;
+        pps_ldisc_ops.open = pps_tty_open;
+        pps_ldisc_ops.close = pps_tty_close;
+
+        err = tty_register_ldisc(N_PPS, &pps_ldisc_ops);
+        if (err)
+                pr_err("can't register PPS line discipline\n");
+        else
+                pr_info("PPS line discipline registered\n");
+
+        return err;
+}
+
+static void __exit pps_tty_cleanup(void)
+{
+        int err;
+
+        err = tty_unregister_ldisc(N_PPS);
+        if (err)
+                pr_err("can't unregister PPS line discipline\n");
+        else
+                pr_info("PPS line discipline removed\n");
+}
+
+module_init(pps_tty_init);
+module_exit(pps_tty_cleanup);
+
+MODULE_ALIAS_LDISC(N_PPS);
+MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
+MODULE_DESCRIPTION("PPS TTY device driver");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 8c3dd36fe91a..78dd1e7120a9 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -491,9 +491,13 @@ uart_handle_dcd_change(struct uart_port *uport, unsigned int status)
 {
         struct uart_state *state = uport->state;
         struct tty_port *port = &state->port;
+        struct tty_ldisc *ld = tty_ldisc_ref(port->tty);
+        struct timespec ts;
 
-        uport->icount.dcd++;
+        if (ld && ld->ops->dcd_change)
+                getnstimeofday(&ts);
 
+        uport->icount.dcd++;
 #ifdef CONFIG_HARD_PPS
         if ((uport->flags & UPF_HARDPPS_CD) && status)
                 hardpps();
@@ -505,6 +509,11 @@ uart_handle_dcd_change(struct uart_port *uport, unsigned int status)
                 else if (port->tty)
                         tty_hangup(port->tty);
         }
+
+        if (ld && ld->ops->dcd_change)
+                ld->ops->dcd_change(port->tty, status, &ts);
+        if (ld)
+                tty_ldisc_deref(ld);
 }
 
 /**