[PATCH v3 5/5] tty: Add software emulated RS485 support for 8250

Matwey V. Kornilov
2015-11-12T14:35:40Z

Implementation of software emulation of RS485 direction handling is based
on omap-serial driver.
Before and after transmission RTS is set to the appropriate value.

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
---
drivers/tty/serial/8250/8250_port.c | 152 ++++++++++++++++++++++++++++++++++--
include/linux/serial_8250.h | 2 +
2 files changed, 148 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 3f6d8a2..b863a12 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -37,6 +37,7 @@
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/pm_runtime.h>
+#include <linux/timer.h>

#include <asm/io.h>
#include <asm/irq.h>
@@ -1299,7 +1300,75 @@ static void serial8250_stop_rx(struct uart_port *port)
serial8250_rpm_put(up);
}

-static inline void __stop_tx(struct uart_8250_port *p)
+static inline void serial8250_rs485_set_rts_on_send(struct uart_8250_port *p)
+{
+ if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND)
+ p->mcr |= UART_MCR_RTS;
+ else
+ p->mcr &= ~UART_MCR_RTS;
+ serial_out(p, UART_MCR, p->mcr);
+}
+
+static inline void serial8250_rs485_set_rts_after_send(struct uart_8250_port *p)
+{
+ if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
+ p->mcr |= UART_MCR_RTS;
+ else
+ p->mcr &= ~UART_MCR_RTS;
+ serial_out(p, UART_MCR, p->mcr);
+}
+
+static __u32 serial8250_rs485_start_tx(struct uart_8250_port *p)
+{
+ if (p->capabilities & UART_CAP_HW485 || !(p->port.rs485.flags & SER_RS485_ENABLED))
+ return 0;
+
+ if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
+ serial8250_stop_rx(&p->port);
+
+ del_timer_sync(&p->rs485_stop_tx_timer);
+
+ if (!!(p->port.rs485.flags & SER_RS485_RTS_ON_SEND) != !!(p->mcr & UART_MCR_RTS)) {
+ serial8250_rs485_set_rts_on_send(p);
+ return p->port.rs485.delay_rts_before_send;
+ }
+
+ return 0;
+}
+
+static inline void __do_stop_tx_rs485(struct uart_8250_port *p)
+{
+ serial8250_rs485_set_rts_after_send(p);
+ /*
+ * Empty the RX FIFO, we are not interested in anything
+ * received during the half-duplex transmission.
+ */
+ if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
+ serial8250_clear_fifos(p);
+}
+
+static void serial8250_handle_rs485_stop_tx_timer(unsigned long arg)
+{
+ struct uart_8250_port *p = (struct uart_8250_port*)arg;
+ __do_stop_tx_rs485(p);
+}
+
+static inline void __stop_tx_rs485(struct uart_8250_port *p)
+{
+ if (p->capabilities & UART_CAP_HW485 || !(p->port.rs485.flags & SER_RS485_ENABLED))
+ return;
+
+ del_timer_sync(&p->rs485_start_tx_timer);
+
+ /* __do_stop_tx_rs485 is going to set RTS according to config AND flush RX FIFO if required */
+ if (p->port.rs485.delay_rts_after_send > 0) {
+ mod_timer(&p->rs485_stop_tx_timer, jiffies + p->port.rs485.delay_rts_after_send * HZ / 1000);
+ } else {
+ __do_stop_tx_rs485(p);
+ }
+}
+
+static inline void __do_stop_tx(struct uart_8250_port *p)
{
if (p->ier & UART_IER_THRI) {
p->ier &= ~UART_IER_THRI;
@@ -1308,6 +1377,12 @@ static inline void __stop_tx(struct uart_8250_port *p)
}
}

+static inline void __stop_tx(struct uart_8250_port *p)
+{
+ __do_stop_tx(p);
+ __stop_tx_rs485(p);
+}
+
static void serial8250_stop_tx(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
@@ -1325,12 +1400,10 @@ static void serial8250_stop_tx(struct uart_port *port)
serial8250_rpm_put(up);
}

-static void serial8250_start_tx(struct uart_port *port)
+static inline void __start_tx(struct uart_port* port)
{
struct uart_8250_port *up = up_to_u8250p(port);

- serial8250_rpm_get_tx(up);
-
if (up->dma && !up->dma->tx_dma(up))
return;

@@ -1356,6 +1429,29 @@ static void serial8250_start_tx(struct uart_port *port)
}
}

+static void serial8250_handle_rs485_start_tx_timer(unsigned long arg)
+{
+ struct uart_port* port = (struct uart_port*)arg;
+ __start_tx(port);
+}
+
+static void serial8250_start_tx(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+ __u32 delay;
+
+ serial8250_rpm_get_tx(up);
+
+ if (timer_pending(&up->rs485_start_tx_timer))
+ return;
+
+ if ((delay = serial8250_rs485_start_tx(up))) {
+ mod_timer(&up->rs485_start_tx_timer, jiffies + delay * HZ / 1000);
+ } else {
+ __start_tx(port);
+ }
+}
+
static void serial8250_throttle(struct uart_port *port)
{
port->throttle(port);
@@ -1806,6 +1902,16 @@ static void serial8250_put_poll_char(struct uart_port *port,

#endif /* CONFIG_CONSOLE_POLL */

+static inline void serial8250_startup_rs485(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+
+ if (up->capabilities & UART_CAP_HW485 || !(up->port.rs485.flags & SER_RS485_ENABLED))
+ return;
+
+ serial8250_rs485_set_rts_after_send(up);
+}
+
int serial8250_do_startup(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
@@ -2044,6 +2150,8 @@ dont_test_tx_en:
inb_p(icp);
}
retval = 0;
+
+ serial8250_startup_rs485(port);
out:
serial8250_rpm_put(up);
return retval;
@@ -2057,12 +2165,24 @@ static int serial8250_startup(struct uart_port *port)
return serial8250_do_startup(port);
}

+static inline void serial8250_shutdown_rs485(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+
+ if (up->capabilities & UART_CAP_HW485 || !(up->port.rs485.flags & SER_RS485_ENABLED))
+ return;
+
+ del_timer_sync(&up->rs485_start_tx_timer);
+ del_timer_sync(&up->rs485_stop_tx_timer);
+}
+
void serial8250_do_shutdown(struct uart_port *port)
{
struct uart_8250_port *up = up_to_u8250p(port);
unsigned long flags;

serial8250_rpm_get(up);
+ serial8250_shutdown_rs485(port);
/*
* Disable interrupts from this port
*/
@@ -2735,11 +2855,23 @@ serial8250_type(struct uart_port *port)
return uart_config[type].name;
}

-static int serial8250_rs485_config(struct uart_port *port,
- struct serial_rs485 *rs485)
+static int serial8250_rs485_config(struct uart_port *port, struct serial_rs485 *rs485)
{
+ bool need_startup = false;
+
+ if (!(port->rs485.flags & SER_RS485_ENABLED) && (rs485->flags & SER_RS485_ENABLED)) {
+ need_startup = true;
+ }
+ if ((port->rs485.flags & SER_RS485_ENABLED) && !(rs485->flags & SER_RS485_ENABLED)) {
+ serial8250_shutdown_rs485(port);
+ }
+
port->rs485 = *rs485;
port->rs485.flags |= SER_RS485_SOFTWARE;
+
+ if (need_startup)
+ serial8250_startup_rs485(port);
+
return 0;
}

@@ -2807,6 +2939,14 @@ void serial8250_set_defaults(struct uart_8250_port *up)
}

up->port.rs485_config = serial8250_rs485_config;
+ init_timer(&up->rs485_stop_tx_timer);
+ up->rs485_stop_tx_timer.function = serial8250_handle_rs485_stop_tx_timer;
+ up->rs485_stop_tx_timer.data = (unsigned long)up;
+ up->rs485_stop_tx_timer.flags |= TIMER_IRQSAFE;
+ init_timer(&up->rs485_start_tx_timer);
+ up->rs485_start_tx_timer.function = serial8250_handle_rs485_start_tx_timer;
+ up->rs485_start_tx_timer.data = (unsigned long)up;
+ up->rs485_start_tx_timer.flags |= TIMER_IRQSAFE;
}
EXPORT_SYMBOL_GPL(serial8250_set_defaults);

diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index faa0e03..c4905e7 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -86,6 +86,8 @@ struct uart_8250_ops {
struct uart_8250_port {
struct uart_port port;
struct timer_list timer; /* "no irq" timer */
+ struct timer_list rs485_start_tx_timer; /* "rs485 start tx" timer */
+ struct timer_list rs485_stop_tx_timer; /* "rs485 stop tx" timer */
struct list_head list; /* ports on this IRQ */
unsigned short capabilities; /* port capabilities */
unsigned short bugs; /* port bugs */
--
2.6.2