Allow use of CTS instead of DCD for PPS line discipline.
Add a "pps_4wire" file to serial ports in sysfs in case the kernel is
configured with CONFIG_PPS_CLIENT_LDISC. Writing 1 to the file enables
the use of CTS instead of DCD for PPS signal input. This is necessary
in case a serial port is not completely wired.
Though this affects PPS processing the patch is against the serial core
as the source of the serial port PPS event dispatching has to be
modified. Furthermore it should be possible to modify the source of
serial port PPS event dispatching before changing the line discipline.
Signed-off-by: Andreas Steinmetz <ast@xxxxxxxx>
diff -rNu linux-4.13.orig/drivers/tty/serial/serial_core.c linux-4.13/drivers/tty/serial/serial_core.c
--- linux-4.13.orig/drivers/tty/serial/serial_core.c 2017-09-03 22:56:17.000000000 +0200
+++ linux-4.13/drivers/tty/serial/serial_core.c 2017-10-10 15:15:04.619941537 +0200
@@ -2664,6 +2664,60 @@
return snprintf(buf, PAGE_SIZE, "%d\n", tmp.iomem_reg_shift);
}
+#ifdef CONFIG_PPS_CLIENT_LDISC
+
+static ssize_t uart_get_pps_4wire(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct tty_port *port = dev_get_drvdata(dev);
+ struct uart_state *state = container_of(port, struct uart_state, port);
+ struct uart_port *uport;
+ int mode = 0;
+
+ mutex_lock(&port->mutex);
+ uport = uart_port_check(state);
+ if (!uport)
+ goto out;
+
+ mode = uport->pps_4wire;
+
+out:
+ mutex_unlock(&port->mutex);
+ return snprintf(buf, PAGE_SIZE, mode ? "yes" : "no");
+}
+
+static ssize_t uart_set_pps_4wire(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t count)
+{
+ struct tty_port *port = dev_get_drvdata(dev);
+ struct uart_state *state = container_of(port, struct uart_state, port);
+ struct uart_port *uport;
+ bool mode;
+ int ret;
+
+ if (!count)
+ return -EINVAL;
+
+ ret = kstrtobool(buf, &mode);
+ if (ret < 0)
+ return ret;
+
+ mutex_lock(&port->mutex);
+ uport = uart_port_check(state);
+ if (!uport)
+ goto out;
+
+ spin_lock_irq(&uport->lock);
+ uport->pps_4wire = mode;
+ spin_unlock_irq(&uport->lock);
+
+out:
+ mutex_unlock(&port->mutex);
+ return count;
+}
+
+#endif
+
static DEVICE_ATTR(type, S_IRUSR | S_IRGRP, uart_get_attr_type, NULL);
static DEVICE_ATTR(line, S_IRUSR | S_IRGRP, uart_get_attr_line, NULL);
static DEVICE_ATTR(port, S_IRUSR | S_IRGRP, uart_get_attr_port, NULL);
@@ -2677,6 +2731,9 @@
static DEVICE_ATTR(io_type, S_IRUSR | S_IRGRP, uart_get_attr_io_type, NULL);
static DEVICE_ATTR(iomem_base, S_IRUSR | S_IRGRP, uart_get_attr_iomem_base, NULL);
static DEVICE_ATTR(iomem_reg_shift, S_IRUSR | S_IRGRP, uart_get_attr_iomem_reg_shift, NULL);
+#ifdef CONFIG_PPS_CLIENT_LDISC
+static DEVICE_ATTR(pps_4wire, 0640, uart_get_pps_4wire, uart_set_pps_4wire);
+#endif
static struct attribute *tty_dev_attrs[] = {
&dev_attr_type.attr,
@@ -2692,6 +2749,9 @@
&dev_attr_io_type.attr,
&dev_attr_iomem_base.attr,
&dev_attr_iomem_reg_shift.attr,
+#ifdef CONFIG_PPS_CLIENT_LDISC
+ &dev_attr_pps_4wire.attr,
+#endif
NULL,
};
@@ -2748,6 +2808,9 @@
goto out;
}
+ /* assert that pps handling is done via DCD as default */
+ uport->pps_4wire = 0;
+
/*
* If this port is a console, then the spinlock is already
* initialised.
@@ -2923,7 +2986,7 @@
lockdep_assert_held_once(&uport->lock);
- if (tty) {
+ if (tty && !uport->pps_4wire) {
ld = tty_ldisc_ref(tty);
if (ld) {
if (ld->ops->dcd_change)
@@ -2952,8 +3015,21 @@
*/
void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
{
+ struct tty_port *port = &uport->state->port;
+ struct tty_struct *tty = port->tty;
+ struct tty_ldisc *ld;
+
lockdep_assert_held_once(&uport->lock);
+ if (tty && uport->pps_4wire) {
+ ld = tty_ldisc_ref(tty);
+ if (ld) {
+ if (ld->ops->dcd_change)
+ ld->ops->dcd_change(tty, status);
+ tty_ldisc_deref(ld);
+ }
+ }
+
uport->icount.cts++;
if (uart_softcts_mode(uport)) {
diff -rNu linux-4.13.orig/include/linux/serial_core.h linux-4.13/include/linux/serial_core.h
--- linux-4.13.orig/include/linux/serial_core.h 2017-09-03 22:56:17.000000000 +0200
+++ linux-4.13/include/linux/serial_core.h 2017-10-10 15:09:04.323454250 +0200
@@ -144,7 +144,7 @@
unsigned char x_char; /* xon/xoff char */
unsigned char regshift; /* reg offset shift */
unsigned char iotype; /* io access style */
- unsigned char unused1;
+ unsigned char pps_4wire; /* CTS instead of DCD */
#define UPIO_PORT (SERIAL_IO_PORT) /* 8b I/O port access */
#define UPIO_HUB6 (SERIAL_IO_HUB6) /* Hub6 ISA card */
--
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