tty: Add software emulated RS485 support for 8250

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@sai.msu.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index d54dcd8..ce587c0 100644 (file)
--- 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 04681e5..01a85a7 100644 (file)
--- 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 +561,73 @@ 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
+ *     &struct 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.
+ *
+ *     See also serial8250_em485_destroy()
+ *
+ *     Return 0 - success, -errno - otherwise
+ */
+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
+ *     &struct 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 +1399,56 @@ 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;
+       struct uart_8250_em485 *em485 = p->em485;
+       unsigned long flags;
+
+       spin_lock_irqsave(&p->port.lock, flags);
+       if (em485 &&
+           em485->active_timer == &em485->stop_tx_timer) {
+               __do_stop_tx_rs485(p);
+               em485->active_timer = NULL;
+       }
+       spin_unlock_irqrestore(&p->port.lock, flags);
+}
+
+static void __stop_tx_rs485(struct uart_8250_port *p)
+{
+       struct uart_8250_em485 *em485 = p->em485;
+
+       if (!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) {
+               em485->active_timer = &em485->stop_tx_timer;
+               mod_timer(&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 +1457,28 @@ static inline void __stop_tx(struct uart_8250_port *p)
        }
 }
 
+static inline void __stop_tx(struct uart_8250_port *p)
+{
+       struct uart_8250_em485 *em485 = p->em485;
+
+       if (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(&em485->start_tx_timer);
+               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 +1496,10 @@ 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 +1525,70 @@ 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);
+       struct uart_8250_em485 *em485 = up->em485;
+       unsigned char mcr;
+
+       if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+               serial8250_stop_rx(&up->port);
+
+       del_timer(&em485->stop_tx_timer);
+       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) {
+                       em485->active_timer = &em485->start_tx_timer;
+                       mod_timer(&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;
+       struct uart_8250_em485 *em485 = p->em485;
+       unsigned long flags;
+
+       spin_lock_irqsave(&p->port.lock, flags);
+       if (em485 &&
+           em485->active_timer == &em485->start_tx_timer) {
+               __start_tx(&p->port);
+               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);
+       struct uart_8250_em485 *em485 = up->em485;
+
+       serial8250_rpm_get_tx(up);
+
+       if (em485 &&
+           em485->active_timer == &em485->start_tx_timer)
+               return;
+
+       if (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 (file)
--- 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)