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.
Note that before calling serial8250_em485_init the caller has to
ensure that UART will interrupt when shift register empty. Otherwise,
emultaion cannot be used.
Both serial8250_em485_init and serial8250_em485_destroy are
idempotent functions.
Signed-off-by: Matwey V. Kornilov <matwey@xxxxxxxxxx>
---
drivers/tty/serial/8250/8250.h | 2 +
drivers/tty/serial/8250/8250_port.c | 211 +++++++++++++++++++++++++++++++++++-
include/linux/serial_8250.h | 8 ++
3 files changed, 217 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index d54dcd8..ce587c0 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -117,6 +117,8 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
struct uart_8250_port *serial8250_get_port(int line);
void serial8250_rpm_get(struct uart_8250_port *p);
void serial8250_rpm_put(struct uart_8250_port *p);
+int serial8250_em485_init(struct uart_8250_port *p);
+void serial8250_em485_destroy(struct uart_8250_port *p);
#if defined(__alpha__) && !defined(CONFIG_PCI)
/*
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index b82fcae..f9442e8 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>
@@ -522,6 +523,20 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
}
}
+static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
+{
+ unsigned char mcr = serial_in(p, UART_MCR);
+
+ if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
+ mcr |= UART_MCR_RTS;
+ else
+ mcr &= ~UART_MCR_RTS;
+ serial_out(p, UART_MCR, mcr);
+}
+
+static void serial8250_em485_handle_start_tx(unsigned long arg);
+static void serial8250_em485_handle_stop_tx(unsigned long arg);
+
void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
{
serial8250_clear_fifos(p);
@@ -546,6 +561,72 @@ void serial8250_rpm_put(struct uart_8250_port *p)
}
EXPORT_SYMBOL_GPL(serial8250_rpm_put);
+/**
+ * serial8250_em485_init - put uart_8250_port into rs485 emulating
+ * @p: uart_8250_port port instance
+ *
+ * The function is used to start rs485 software emulating on the
+ * uart_8250_port @p. Namely, RTS is switched before/after transmission.
+ * The function is idempotent, so it is safe to call it multiple times.
+ *
+ * The caller MUST enable interrupt on empty shift register before
+ * calling serial8250_em485_init. This interrupt is not a part of
+ * 8250 standard, but implementation defined.
+ *
+ * The function is supposed to be called from .rs485_config callback
+ * or from any other callback protected with p->port.lock spinlock.
+ *
+ * The return value is negative error code or 0 on succes.
+ *
+ * See also serial8250_em485_destroy
+ */
+int serial8250_em485_init(struct uart_8250_port *p)
+{
+ if (p->em485 != NULL)
+ return 0;
+
+ p->em485 = kmalloc(sizeof(struct uart_8250_em485), GFP_KERNEL);
+ if (p->em485 == NULL)
+ return -ENOMEM;
+
+ setup_timer(&p->em485->stop_tx_timer,
+ serial8250_em485_handle_stop_tx, (unsigned long)p);
+ setup_timer(&p->em485->start_tx_timer,
+ serial8250_em485_handle_start_tx, (unsigned long)p);
+ p->em485->active_timer = NULL;
+
+ serial8250_em485_rts_after_send(p);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(serial8250_em485_init);
+
+/**
+ * serial8250_em485_destroy - put uart_8250_port into normal state
+ * @p: uart_8250_port port instance
+ *
+ * The function is used to stop rs485 software emulating on the
+ * uart_8250_port @p. The function is idempotent, so it is safe to
+ * call it multiple times.
+ *
+ * The function is supposed to be called from rs485_config callback
+ * or from any other callback protected with p->port.lock spinlock.
+ *
+ * See also serial8250_em485_init
+ */
+void serial8250_em485_destroy(struct uart_8250_port *p)
+{
+ if (p->em485 == NULL)
+ return;
+
+ del_timer(&p->em485->start_tx_timer);
+ del_timer(&p->em485->stop_tx_timer);
+
+ kfree(p->em485);
+ p->em485 = NULL;
+}
+EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
+
/*
* These two wrappers ensure that enable_runtime_pm_tx() can be called more than
* once and disable_runtime_pm_tx() will still disable RPM because the fifo is
@@ -1317,7 +1398,52 @@ static void serial8250_stop_rx(struct uart_port *port)
serial8250_rpm_put(up);
}
-static inline void __stop_tx(struct uart_8250_port *p)
+static void __do_stop_tx_rs485(struct uart_8250_port *p)
+{
+ if (!p->em485)
+ return;
+
+ serial8250_em485_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_em485_handle_stop_tx(unsigned long arg)
+{
+ struct uart_8250_port *p = (struct uart_8250_port *)arg;
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->port.lock, flags);
+ if (p->em485 &&
+ p->em485->active_timer == &p->em485->stop_tx_timer) {
+ __do_stop_tx_rs485(p);
+ p->em485->active_timer = NULL;
+ }
+ spin_unlock_irqrestore(&p->port.lock, flags);
+}
+
+static void __stop_tx_rs485(struct uart_8250_port *p)
+{
+ if (!p->em485)
+ return;
+
+ /* __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) {
+ p->em485->active_timer = &p->em485->stop_tx_timer;
+ mod_timer(&p->em485->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;
@@ -1326,6 +1452,24 @@ static inline void __stop_tx(struct uart_8250_port *p)
}
}
+static inline void __stop_tx(struct uart_8250_port *p)
+{
+ if (p->em485) {
+ unsigned char lsr = serial_in(p, UART_LSR);
+ /* To provide required timeing and allow FIFO transfer,
+ * __stop_tx_rs485 must be called only when both FIFO and shift register
+ * are empty. It is for device driver to enable interrupt on TEMT.
+ */
+ if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
+ return;
+
+ del_timer(&p->em485->start_tx_timer);
+ p->em485->active_timer = NULL;
+ }
+ __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);
@@ -1343,12 +1487,10 @@ 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;
@@ -1374,6 +1516,67 @@ static void serial8250_start_tx(struct uart_port *port)
}
}
+static inline void start_tx_rs485(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+ unsigned char mcr;
+
+ if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+ serial8250_stop_rx(&up->port);
+
+ del_timer(&up->em485->stop_tx_timer);
+ up->em485->active_timer = NULL;
+
+ mcr = serial_in(up, UART_MCR);
+ if (!!(up->port.rs485.flags & SER_RS485_RTS_ON_SEND) !=
+ !!(mcr & UART_MCR_RTS)) {
+ if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
+ mcr |= UART_MCR_RTS;
+ else
+ mcr &= ~UART_MCR_RTS;
+ serial_out(up, UART_MCR, mcr);
+
+ if (up->port.rs485.delay_rts_before_send > 0) {
+ up->em485->active_timer = &up->em485->start_tx_timer;
+ mod_timer(&up->em485->start_tx_timer, jiffies +
+ up->port.rs485.delay_rts_before_send * HZ / 1000);
+ return;
+ }
+ }
+
+ __start_tx(port);
+}
+
+static void serial8250_em485_handle_start_tx(unsigned long arg)
+{
+ struct uart_8250_port *p = (struct uart_8250_port *)arg;
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->port.lock, flags);
+ if (p->em485 &&
+ p->em485->active_timer == &p->em485->start_tx_timer) {
+ __start_tx(&p->port);
+ p->em485->active_timer = NULL;
+ }
+ spin_unlock_irqrestore(&p->port.lock, flags);
+}
+
+static void serial8250_start_tx(struct uart_port *port)
+{
+ struct uart_8250_port *up = up_to_u8250p(port);
+
+ serial8250_rpm_get_tx(up);
+
+ if (up->em485 &&
+ up->em485->active_timer == &up->em485->start_tx_timer)
+ return;
+
+ if (up->em485)
+ start_tx_rs485(port);
+ else
+ __start_tx(port);
+}
+
static void serial8250_throttle(struct uart_port *port)
{
port->throttle(port);
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index faa0e03..4348797 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -76,6 +76,12 @@ struct uart_8250_ops {
void (*release_irq)(struct uart_8250_port *);
};
+struct uart_8250_em485 {
+ struct timer_list start_tx_timer; /* "rs485 start tx" timer */
+ struct timer_list stop_tx_timer; /* "rs485 stop tx" timer */
+ struct timer_list *active_timer; /* pointer to active timer */
+};
+
/*
* This should be used by drivers which want to register
* their own 8250 ports without registering their own
@@ -122,6 +128,8 @@ struct uart_8250_port {
/* 8250 specific callbacks */
int (*dl_read)(struct uart_8250_port *);
void (*dl_write)(struct uart_8250_port *, int);
+
+ struct uart_8250_em485 *em485;
};
static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
--
2.7.0
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
