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There's systems around that only have incompletely wired serial ports,
e.g. the CompuLab Intense PC3 which only has 4 wire serial ports (RxD,
TxD, RTS, CTS).
The kernel currently only supports DCD for the PPS line discipline.
The attached patch adds a configuration option that allows CTS to be
used instead of DCD for the PPS line discipline for 8250/16x50 based
serial ports.
It may look a bit ugly but it seems to me to be the least intrusive way
to enable the use of the kernel PPS line discipline for machines with
incompletely wired serial ports.
The patch is actually against 4.12.10 (sorry for the older kernel) and
tested with gpsd on a CompuLab Intense PC3.
--
Andreas Steinmetz SPAMmers use robotrap@xxxxxxxx
--- linux.orig/drivers/tty/serial/serial_core.c 2017-09-19 22:15:00.655700355 +0200
+++ linux/drivers/tty/serial/serial_core.c 2017-09-19 22:15:05.748732334 +0200
@@ -2920,10 +2920,13 @@
{
struct tty_port *port = &uport->state->port;
struct tty_struct *tty = port->tty;
+#ifndef CONFIG_PPS_CLIENT_LDISC_CTS
struct tty_ldisc *ld;
+#endif
lockdep_assert_held_once(&uport->lock);
+#ifndef CONFIG_PPS_CLIENT_LDISC_CTS
if (tty) {
ld = tty_ldisc_ref(tty);
if (ld) {
@@ -2932,6 +2935,7 @@
tty_ldisc_deref(ld);
}
}
+#endif
uport->icount.dcd++;
@@ -2953,8 +2957,25 @@
*/
void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
{
+#ifdef CONFIG_PPS_CLIENT_LDISC_CTS
+ struct tty_port *port = &uport->state->port;
+ struct tty_struct *tty = port->tty;
+ struct tty_ldisc *ld;
+#endif
+
lockdep_assert_held_once(&uport->lock);
+#ifdef CONFIG_PPS_CLIENT_LDISC_CTS
+ if (tty) {
+ ld = tty_ldisc_ref(tty);
+ if (ld) {
+ if (ld->ops->dcd_change)
+ ld->ops->dcd_change(tty, status);
+ tty_ldisc_deref(ld);
+ }
+ }
+#endif
+
uport->icount.cts++;
if (uart_softcts_mode(uport)) {
--- linux.orig/drivers/pps/clients/Kconfig 2017-09-19 22:20:20.877737479 +0200
+++ linux/drivers/pps/clients/Kconfig 2017-09-19 22:23:27.129039073 +0200
@@ -22,6 +22,15 @@
If you say yes here you get support for a PPS source connected
with the CD (Carrier Detect) pin of your serial port.
+config PPS_CLIENT_LDISC_CTS
+ tristate "PPS line discipline uses CTS"
+ depends on SERIAL_8250 && PPS_CLIENT_LDISC
+ help
+ If you say yes here the CTS (Clear To Send) pin of your serial
+ port will be used instead of the CD (Carrier Detect) pin.
+ Useful for machines that only have four wire serial ports.
+ If in doubt, say N.
+
config PPS_CLIENT_PARPORT
tristate "Parallel port PPS client"
depends on PPS && PARPORT
