[PATCH 10/15] serial: 8250_mxpcie: defer uart_write_wakeup() to workqueue

[Crescent Hsieh]

Avoid calling uart_write_wakeup() directly from the interrupt-driven TX
path.

Defer the wakeup to a per-port work item and coalesce multiple TX events
using a pending flag, so only one wakeup is scheduled while a previous
one is still outstanding.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@xxxxxxxx>
---
 drivers/tty/serial/8250/8250_mxpcie.c | 34 +++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_mxpcie.c b/drivers/tty/serial/8250/8250_mxpcie.c
index 19233c3c5f1f..8dc1b7b0af04 100644
--- a/drivers/tty/serial/8250/8250_mxpcie.c
+++ b/drivers/tty/serial/8250/8250_mxpcie.c
@@ -18,6 +18,7 @@
 #include <linux/serial_core.h>
 #include <linux/serial_reg.h>
 #include <linux/tty_flip.h>
+#include <linux/workqueue.h>
 #include <linux/8250_pci.h>
 
 #include "8250.h"
@@ -105,8 +106,13 @@
 #define MOXA_EVEN_RS_MASK	GENMASK(3, 0)
 #define MOXA_ODD_RS_MASK	GENMASK(7, 4)
 
+#define MOXA_EVENT_TXLOW	BIT(0)
+
 struct mxpcie8250_port {
 	int line;
+	unsigned long event_flags;
+	struct uart_port *port;
+	struct work_struct work;
 };
 
 struct mxpcie8250 {
@@ -327,6 +333,8 @@ static void mxpcie8250_tx_chars(struct uart_8250_port *up)
 {
 	struct uart_port *port = &up->port;
 	struct tty_port *tport = &port->state->port;
+	struct device *dev = port->dev;
+	struct mxpcie8250 *priv = dev_get_drvdata(dev);
 	unsigned int i, count, txsize;
 	unsigned char c;
 
@@ -347,9 +355,10 @@ static void mxpcie8250_tx_chars(struct uart_8250_port *up)
 
 		serial_out(up, MOXA_PUART_TX_FIFO_MEM + i, c);
 	}
-	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
-		uart_write_wakeup(port);
-
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS) {
+		if (!test_and_set_bit(MOXA_EVENT_TXLOW, &priv->port[port->port_id].event_flags))
+			schedule_work(&priv->port[port->port_id].work);
+	}
 	if (kfifo_is_empty(&tport->xmit_fifo) && !(up->capabilities & UART_CAP_RPM))
 		port->ops->stop_tx(port);
 }
@@ -381,6 +390,14 @@ static int mxpcie8250_handle_irq(struct uart_port *port)
 	return 1;
 }
 
+static void mxpcie8250_work_handler(struct work_struct *work)
+{
+	struct mxpcie8250_port *priv_port = container_of(work, struct mxpcie8250_port, work);
+
+	if (test_and_clear_bit(MOXA_EVENT_TXLOW, &priv_port->event_flags))
+		uart_write_wakeup(priv_port->port);
+}
+
 static void mxpcie8250_init_board(struct pci_dev *pdev, struct mxpcie8250 *priv)
 {
 	void __iomem *bar2_base = priv->bar2_base;
@@ -436,7 +453,7 @@ static void mxpcie8250_setup_port(struct pci_dev *pdev,
 static int mxpcie8250_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 {
 	struct device *dev = &pdev->dev;
-	struct uart_8250_port up = {};
+	struct uart_8250_port up = {}, *new_port;
 	struct mxpcie8250 *priv;
 	unsigned short device = pdev->device;
 	unsigned int i, num_ports;
@@ -496,6 +513,11 @@ static int mxpcie8250_probe(struct pci_dev *pdev, const struct pci_device_id *id
 				up.port.iotype, priv->port[i].line);
 			break;
 		}
+		new_port = serial8250_get_port(priv->port[i].line);
+
+		priv->port[i].port = &new_port->port;
+
+		INIT_WORK(&priv->port[i].work, mxpcie8250_work_handler);
 	}
 	dev_set_drvdata(dev, priv);
 
@@ -507,8 +529,10 @@ static void mxpcie8250_remove(struct pci_dev *pdev)
 	struct mxpcie8250 *priv = dev_get_drvdata(&pdev->dev);
 	unsigned int i;
 
-	for (i = 0; i < priv->num_ports; i++)
+	for (i = 0; i < priv->num_ports; i++) {
+		cancel_work_sync(&priv->port[i].work);
 		serial8250_unregister_port(priv->port[i].line);
+	}
 }
 
 static const struct pci_device_id mxpcie8250_pci_ids[] = {
-- 
2.43.0