serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

index 69932b7..c945ceb 100644
@@ -531,11 +531,9 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
 
 void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
 {
-	unsigned char fcr;
-
 	serial8250_clear_fifos(p);
-	fcr = uart_config[p->port.type].fcr;
-	serial_out(p, UART_FCR, fcr);
+	p->fcr = uart_config[p->port.type].fcr;
+	serial_out(p, UART_FCR, p->fcr);
 }
 EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
 

@@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 		if ((baud < 2400 && !up->dma) || fifo_bug) {
 			fcr &= ~UART_FCR_TRIGGER_MASK;
 			fcr |= UART_FCR_TRIGGER_1;
+			/* Don't use user setting RX trigger */
+			up->fcr = 0;
 		}
 	}
 
 	/*
+	 * If up->fcr exists, a user has opened this port, changed RX trigger,
+	 * or read RX trigger before. So, we don't need to change up->fcr here.
+	 */
+	if (!up->fcr)
+		up->fcr = fcr;
+
+	/*
 	 * MCR-based auto flow control.  When AFE is enabled, RTS will be
 	 * deasserted when the receive FIFO contains more characters than
 	 * the trigger, or the MCR RTS bit is cleared.  In the case where

@@ -2455,15 +2462,15 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 	 * is written without DLAB set, this mode will be disabled.
 	 */
 	if (port->type == PORT_16750)
-		serial_port_out(port, UART_FCR, fcr);
+		serial_port_out(port, UART_FCR, up->fcr);
 
 	serial_port_out(port, UART_LCR, cval);		/* reset DLAB */
 	up->lcr = cval;					/* Save LCR */
 	if (port->type != PORT_16750) {
 		/* emulated UARTs (Lucent Venus 167x) need two steps */
-		if (fcr & UART_FCR_ENABLE_FIFO)
+		if (up->fcr & UART_FCR_ENABLE_FIFO)
 			serial_port_out(port, UART_FCR, UART_FCR_ENABLE_FIFO);
-		serial_port_out(port, UART_FCR, fcr);		/* set fcr */
+		serial_port_out(port, UART_FCR, up->fcr);	/* set fcr */
 	}
 	serial8250_set_mctrl(port, port->mctrl);
 	spin_unlock_irqrestore(&port->lock, flags);

@@ -2656,6 +2663,172 @@ static int serial8250_request_port(struct uart_port *port)
 	return ret;
 }
 
+static unsigned char convert_fcr2val(struct uart_8250_port *up,
+				     unsigned char fcr)
+{
+	unsigned char val = 0, trig_raw = fcr & UART_FCR_TRIGGER_MASK;
+
+	switch (up->port.type) {
+	case PORT_16550A:
+		if (trig_raw == UART_FCR_R_TRIG_00)
+			val = 1;
+		else if (trig_raw == UART_FCR_R_TRIG_01)
+			val = 4;
+		else if (trig_raw == UART_FCR_R_TRIG_10)
+			val = 8;
+		else if (trig_raw == UART_FCR_R_TRIG_11)
+			val = 14;
+		break;
+	}
+	return val;
+}
+
+static int convert_val2rxtrig(struct uart_8250_port *up, unsigned char val)
+{
+	switch (up->port.type) {
+	case PORT_16550A:
+		if (val == 1)
+			return UART_FCR_R_TRIG_00;
+		else if (val == 4)
+			return UART_FCR_R_TRIG_01;
+		else if (val == 8)
+			return UART_FCR_R_TRIG_10;
+		else if (val == 14)
+			return UART_FCR_R_TRIG_11;
+		break;
+	default:
+		pr_info("Not support RX-trigger setting for this serial %u\n",
+			up->port.type);
+	}
+	return -EINVAL;
+}
+
+static unsigned char do_get_rx_int_trig(struct tty_port *port)
+{
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct uart_port *uport = state->uart_port;
+	struct uart_8250_port *up =
+		container_of(uport, struct uart_8250_port, port);
+
+	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
+		return 0;
+
+	if (!up->fcr)
+		/* termios is not set yet */
+		up->fcr = uart_config[up->port.type].fcr;
+
+	return convert_fcr2val(up, up->fcr);
+}
+
+static unsigned char do_serial8250_get_rx_int_trig(struct tty_port *port)
+{
+	unsigned char rx_trig_byte;
+
+	mutex_lock(&port->mutex);
+	rx_trig_byte = do_get_rx_int_trig(port);
+	mutex_unlock(&port->mutex);
+
+	return rx_trig_byte;
+}
+
+static ssize_t serial8250_get_attr_rx_int_trig(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct tty_port *port = dev_get_drvdata(dev);
+	unsigned char rx_trig_byte;
+
+	rx_trig_byte = do_serial8250_get_rx_int_trig(port);
+	/* rx_trig_byte == 0 means RX interrupt trigger is undefined */
+	if (!rx_trig_byte)
+		return -EINVAL;
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", rx_trig_byte);
+}
+
+static int do_set_rx_int_trig(struct tty_port *port, unsigned char val)
+{
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct uart_port *uport = state->uart_port;
+	struct uart_8250_port *up =
+		container_of(uport, struct uart_8250_port, port);
+	unsigned char fcr;
+	int rx_trig;
+
+	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
+		return -EINVAL;
+
+	rx_trig = convert_val2rxtrig(up, val);
+	if (rx_trig < 0)
+		return rx_trig;
+
+	serial8250_clear_fifos(up);
+	if (!up->fcr)
+		/* termios is not set yet */
+		fcr = uart_config[up->port.type].fcr;
+	else
+		fcr = up->fcr;
+	fcr &= ~UART_FCR_TRIGGER_MASK;
+	fcr |= (unsigned char)rx_trig;
+	up->fcr = fcr;
+	serial_out(up, UART_FCR, up->fcr);
+	return 0;
+}
+
+static int do_serial8250_set_rx_int_trig(struct tty_port *port,
+					 unsigned char val)
+{
+	int ret;
+
+	mutex_lock(&port->mutex);
+	ret = do_set_rx_int_trig(port, val);
+	mutex_unlock(&port->mutex);
+
+	return ret;
+}
+
+static ssize_t serial8250_set_attr_rx_int_trig(struct device *dev,
+	struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct tty_port *port = dev_get_drvdata(dev);
+	unsigned char val;
+	int ret;
+
+	if (!count)
+		return -EINVAL;
+
+	ret = kstrtou8(buf, 10, &val);
+	if (ret < 0)
+		return ret;
+
+	ret = do_serial8250_set_rx_int_trig(port, val);
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+
+static DEVICE_ATTR(rx_int_trig, S_IRUSR | S_IWUSR | S_IRGRP,
+		   serial8250_get_attr_rx_int_trig,
+		   serial8250_set_attr_rx_int_trig);
+
+static struct attribute *serial8250_dev_attrs[] = {
+	&dev_attr_rx_int_trig.attr,
+	NULL,
+	};
+
+static struct attribute_group serial8250_dev_attr_group = {
+	.attrs = serial8250_dev_attrs,
+	};
+
+static void register_dev_spec_attr_grp(struct uart_8250_port *up)
+{
+	switch (up->port.type) {
+	case PORT_16550A:
+		up->port.dev_spec_attr_group = &serial8250_dev_attr_group;
+		break;
+	}
+}
+
 static void serial8250_config_port(struct uart_port *port, int flags)
 {
 	struct uart_8250_port *up =

@@ -2704,6 +2877,8 @@ static void serial8250_config_port(struct uart_port *port, int flags)
 	if ((port->type == PORT_XR17V35X) ||
 	   (port->type == PORT_XR17D15X))
 		port->handle_irq = exar_handle_irq;
+
+	register_dev_spec_attr_grp(up);
 }
 
 static int

index ece2049..5cfa732 100644
@@ -2548,15 +2548,16 @@ static struct attribute *tty_dev_attrs[] = {
 	NULL,
 	};
 
-static const struct attribute_group tty_dev_attr_group = {
+static struct attribute_group tty_dev_attr_group = {
 	.attrs = tty_dev_attrs,
 	};
 
-static const struct attribute_group *tty_dev_attr_groups[] = {
-	&tty_dev_attr_group,
-	NULL
-	};
-
+static void make_uport_attr_grps(struct uart_port *uport)
+{
+	uport->attr_grps[0] = &tty_dev_attr_group;
+	if (uport->dev_spec_attr_group)
+		uport->attr_grps[1] = uport->dev_spec_attr_group;
+}
 
 /**
  *	uart_add_one_port - attach a driver-defined port structure

@@ -2607,12 +2608,15 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 
 	uart_configure_port(drv, state, uport);
 
+	make_uport_attr_grps(uport);
+
 	/*
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this ports parameters.
 	 */
 	tty_dev = tty_port_register_device_attr(port, drv->tty_driver,
-			uport->line, uport->dev, port, tty_dev_attr_groups);
+			uport->line, uport->dev, port,
+			(const struct attribute_group **)uport->attr_grps);
 	if (likely(!IS_ERR(tty_dev))) {
 		device_set_wakeup_capable(tty_dev, 1);
 	} else {

index af47a8a..2ce1152 100644
@@ -76,6 +76,7 @@ struct uart_8250_port {
 	unsigned short		bugs;		/* port bugs */
 	unsigned int		tx_loadsz;	/* transmit fifo load size */
 	unsigned char		acr;
+	unsigned char		fcr;
 	unsigned char		ier;
 	unsigned char		lcr;
 	unsigned char		mcr;

index f729be9..7e3122f 100644
@@ -113,6 +113,8 @@ struct uart_icount {
 
 typedef unsigned int __bitwise__ upf_t;
 
+#define MAX_ATTR_GRPS		3
+
 struct uart_port {
 	spinlock_t		lock;			/* port lock */
 	unsigned long		iobase;			/* in/out[bwl] */

@@ -195,6 +197,8 @@ struct uart_port {
 	unsigned int		line;			/* port index */
 	resource_size_t		mapbase;		/* for ioremap */
 	struct device		*dev;			/* parent device */
+	struct attribute_group	*dev_spec_attr_group;	/* specific attribute */
+	struct attribute_group	*attr_grps[MAX_ATTR_GRPS];/* all attr. groups */
 	unsigned char		hub6;			/* this should be in the 8250 driver */
 	unsigned char		suspended;
 	unsigned char		irq_wake;