[PATCH RFC v2 2/3] tty: serial_core: Add hooks for uart slave drivers

[Marek Belisko <marek@goldelico.com>]

From: "H. Nikolaus Schaller" <hns@goldelico.com>

1. allow drivers to get notified in mctrl changes
2. allow drivers to get notified on rx data (indicating to the driver that
   the connected chip is active)

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Marek Belisko <marek@goldelico.com>
---
 drivers/tty/serial/serial_core.c | 102 +++++++++++++++++++++++++++++++++++++--
 include/linux/serial_core.h      |  11 ++++-
 2 files changed, 107 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index ad61441..c8910c4 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -163,6 +163,84 @@ err0:
 }
 EXPORT_SYMBOL_GPL(devm_serial_get_uart_by_phandle);
 
+void uart_register_slave(struct uart_port *uport, void *slave)
+{
+	if (!slave) {
+		uart_register_mctrl_notification(uport, NULL);
+		uart_register_rx_notification(uport, NULL, NULL);
+	}
+	uport->slave = slave;
+}
+
+void uart_register_mctrl_notification(struct uart_port *uport, int (*function)(void *slave, int state))
+{
+	uport->mctrl_notification = function;
+}
+
+static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
+		int init_hw);
+
+static void uart_port_shutdown(struct tty_port *port);
+
+void uart_register_rx_notification(struct uart_port *uport, int (*function)(void *slave, unsigned int *c), struct ktermios *termios)
+{
+	struct uart_state *state = uport->state;
+	struct tty_port *tty_port = &state->port;
+
+	if (!uport->slave)
+		return;	/* slave must be registered first */
+
+	uport->rx_notification = function;
+
+	if (tty_port->count == 0) {
+		if (function) {
+			int retval = 0;
+
+			uart_change_pm(state, UART_PM_STATE_ON);
+			retval = uport->ops->startup(uport);
+			if (retval == 0 && termios) {
+				int hw_stopped;
+				/*
+				 * Initialise the hardware port settings.
+				 */
+				uport->ops->set_termios(uport, termios, NULL);
+
+				/*
+				 * Set modem status enables based on termios cflag
+				 */
+				spin_lock_irq(&uport->lock);
+				if (termios->c_cflag & CRTSCTS)
+					uport->status |= UPSTAT_CTS_ENABLE;
+				else
+					uport->status &= ~UPSTAT_CTS_ENABLE;
+
+				if (termios->c_cflag & CLOCAL)
+					uport->status &= ~UPSTAT_DCD_ENABLE;
+				else
+					uport->status |= UPSTAT_DCD_ENABLE;
+
+				/* reset sw-assisted CTS flow control based on (possibly) new mode */
+				hw_stopped = uport->hw_stopped;
+				uport->hw_stopped = uart_softcts_mode(uport) &&
+					!(uport->ops->get_mctrl(uport) & TIOCM_CTS);
+				if (uport->hw_stopped) {
+					if (!hw_stopped)
+						uport->ops->stop_tx(uport);
+				} else {
+					if (hw_stopped)
+						uport->ops->start_tx(uport);
+				}
+				spin_unlock_irq(&uport->lock);
+			}
+		} else
+			uart_port_shutdown(tty_port);
+	}
+}
+
+EXPORT_SYMBOL_GPL(uart_register_slave);
+EXPORT_SYMBOL_GPL(uart_register_mctrl_notification);
+EXPORT_SYMBOL_GPL(uart_register_rx_notification);
+
 /*
  * This routine is used by the interrupt handler to schedule processing in
  * the software interrupt portion of the driver.
@@ -220,6 +298,10 @@ uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
 	port->mctrl = (old & ~clear) | set;
 	if (old != port->mctrl)
 		port->ops->set_mctrl(port, port->mctrl);
+
+	if (port->mctrl_notification)
+		(*port->mctrl_notification)(port->slave, port->mctrl);
+
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
@@ -259,7 +341,8 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 		uart_circ_clear(&state->xmit);
 	}
 
-	retval = uport->ops->startup(uport);
+	if (!state->uart_port->rx_notification)
+		retval = uport->ops->startup(uport);
 	if (retval == 0) {
 		if (uart_console(uport) && uport->cons->cflag) {
 			tty->termios.c_cflag = uport->cons->cflag;
@@ -295,7 +378,7 @@ static int uart_startup(struct tty_struct *tty, struct uart_state *state,
 		int init_hw)
 {
 	struct tty_port *port = &state->port;
-	int retval;
+	int retval = 0;
 
 	if (port->flags & ASYNC_INITIALIZED)
 		return 0;
@@ -341,8 +424,12 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 
 		if (!tty || (tty->termios.c_cflag & HUPCL))
 			uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
-
-		uart_port_shutdown(port);
+		/*
+		 * if we have a slave that has registered for rx_notifications
+		 * we do not shut down the uart port to be able to monitor the device
+		 */
+		if (!uport->rx_notification)
+			uart_port_shutdown(port);
 	}
 
 	/*
@@ -1489,8 +1576,9 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
 	/*
 	 * At this point, we stop accepting input.  To do this, we
 	 * disable the receive line status interrupts.
+	 * Unless a slave driver wants to keep input running
 	 */
-	if (port->flags & ASYNC_INITIALIZED) {
+	if (!uport->rx_notification && (port->flags & ASYNC_INITIALIZED)) {
 		unsigned long flags;
 		spin_lock_irqsave(&uport->lock, flags);
 		uport->ops->stop_rx(uport);
@@ -3018,6 +3106,10 @@ void uart_insert_char(struct uart_port *port, unsigned int status,
 {
 	struct tty_port *tport = &port->state->port;
 
+	if (port->rx_notification)
+		if ((*port->rx_notification)(port->slave, &ch))
+			return;	/* slave told us to ignore character */
+
 	if ((status & port->ignore_status_mask & ~overrun) == 0)
 		if (tty_insert_flip_char(tport, ch, flag) == 0)
 			++port->icount.buf_overrun;
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index ba23718..77029781 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -35,7 +35,7 @@
 #define uart_console(port) \
 	((port)->cons && (port)->cons->index == (port)->line)
 #else
-#define uart_console(port)      ({ (void)port; 0; })
+#define uart_console(port)      (0)
 #endif
 
 struct uart_port;
@@ -247,7 +247,11 @@ struct uart_port {
 	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
 	struct serial_rs485     rs485;
 	void			*private_data;		/* generic platform data pointer */
+	/* UART slave support */
 	struct list_head	head;			/* list of uarts e.g. to look up by phandle */
+	void			*slave;			/* optional slave (there can be only one) */
+	int			(*mctrl_notification)(void *slave, int state);
+	int			(*rx_notification)(void *slave, unsigned int *c);
 };
 
 static inline int serial_port_in(struct uart_port *up, int offset)
@@ -485,4 +489,9 @@ static inline int uart_handle_break(struct uart_port *port)
  */
 extern struct uart_port *devm_serial_get_uart_by_phandle(struct device *dev,
 		const char *phandle, u8 index);
+/* register to receive notifications */
+extern void uart_register_slave(struct uart_port *uart, void *slave);
+extern void uart_register_mctrl_notification(struct uart_port *uart, int (*function)(void *slave, int state));
+extern void uart_register_rx_notification(struct uart_port *uart, int (*function)(void *slave, unsigned int *c), struct ktermios *termios);
+
 #endif /* LINUX_SERIAL_CORE_H */
-- 
1.9.1