[PATCH v1 3/3] serial: liteuart: add IRQ support

[Gabriel Somlo <gsomlo@gmail.com>]

Add support for IRQ-driven RX. The TX path remains "polling" based,
which is fine since TX is synchronous.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
---
 drivers/tty/serial/liteuart.c | 65 +++++++++++++++++++++++++++++++----
 1 file changed, 58 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
index 90a29ed79bff..47ce3ecc50f2 100644
--- a/drivers/tty/serial/liteuart.c
+++ b/drivers/tty/serial/liteuart.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/console.h>
+#include <linux/interrupt.h>
 #include <linux/litex.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -90,13 +91,27 @@ static void liteuart_rx_chars(struct uart_port *port)
 	tty_flip_buffer_push(&port->state->port);
 }
 
+static irqreturn_t liteuart_interrupt(int irq, void *data)
+{
+	struct uart_port *port = data;
+	unsigned int isr;
+
+	isr = litex_read32(port->membase + OFF_EV_PENDING);
+
+	spin_lock(&port->lock);
+	if (isr & EV_RX)
+		liteuart_rx_chars(port);
+	spin_unlock(&port->lock);
+
+	return IRQ_RETVAL(isr);
+}
+
 static void liteuart_timer(struct timer_list *t)
 {
 	struct liteuart_port *uart = from_timer(uart, t, timer);
 	struct uart_port *port = &uart->port;
 
-	liteuart_rx_chars(port);
-
+	liteuart_interrupt(0, port);
 	mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
 }
 
@@ -165,19 +180,48 @@ static void liteuart_stop_rx(struct uart_port *port)
 static int liteuart_startup(struct uart_port *port)
 {
 	struct liteuart_port *uart = to_liteuart_port(port);
+	unsigned long flags;
+	int ret;
+	u8 irq_mask = 0;
 
-	/* disable events */
-	litex_write8(port->membase + OFF_EV_ENABLE, 0);
+	if (port->irq) {
+		ret = request_irq(port->irq, liteuart_interrupt, 0,
+				  DRV_NAME, port);
+		if (ret == 0) {
+			/* we only need interrupts on the rx path! */
+			irq_mask = EV_RX;
+		} else {
+			pr_err(DRV_NAME ": can't attach LiteUART %d irq=%d; "
+			       "switching to polling\n", port->line, port->irq);
+			port->irq = 0;
+		}
+	}
 
-	/* prepare timer for polling */
-	timer_setup(&uart->timer, liteuart_timer, 0);
-	mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
+	if (!port->irq) {
+		timer_setup(&uart->timer, liteuart_timer, 0);
+		mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
+	}
+
+	spin_lock_irqsave(&port->lock, flags);
+	litex_write8(port->membase + OFF_EV_ENABLE, irq_mask);
+	spin_unlock_irqrestore(&port->lock, flags);
 
 	return 0;
 }
 
 static void liteuart_shutdown(struct uart_port *port)
 {
+	struct liteuart_port *uart = to_liteuart_port(port);
+	unsigned long flags;
+
+	spin_lock_irqsave(&port->lock, flags);
+	litex_write8(port->membase + OFF_EV_ENABLE, 0);
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	if (port->irq)
+		free_irq(port->irq, port);
+	else
+		del_timer_sync(&uart->timer);
 }
 
 static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
@@ -266,6 +310,13 @@ static int liteuart_probe(struct platform_device *pdev)
 		goto err_erase_id;
 	}
 
+	/* get irq */
+	ret = platform_get_irq_optional(pdev, 0);
+	if (ret < 0 && ret != -ENXIO)
+		return ret;
+	if (ret > 0)
+		port->irq = ret;
+
 	/* values not from device tree */
 	port->dev = &pdev->dev;
 	port->iotype = UPIO_MEM;
-- 
2.37.3