[PATCH v5 06/14] serial: 8250_mxpcie: add custom handle_irq callback

Add a mxpcie-specific handle_irq() implementation for Moxa PCIe serial
ports.

This keeps the interrupt handling self-contained in the driver and
provides a hook point for MUEx50-specific RX/TX paths added in subsequent
patches. The handler processes RX, updates modem status, and handles TX
when THRE is asserted.

Signed-off-by: Crescent Hsieh <[email protected]>
---
 drivers/tty/serial/8250/8250_mxpcie.c | 42 +++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_mxpcie.c b/drivers/tty/serial/8250/8250_mxpcie.c
index 39eee8a9b82d..9190825ff3d3 100644
--- a/drivers/tty/serial/8250/8250_mxpcie.c
+++ b/drivers/tty/serial/8250/8250_mxpcie.c
@@ -263,6 +263,47 @@ static void mxpcie8250_unthrottle(struct uart_port *port)
 	serial_out(up, UART_IER, up->ier);
 }
 
+static bool mxpcie8250_should_rx(struct uart_8250_port *up, u16 lsr)
+{
+	struct uart_port *port = &up->port;
+
+	if (!(lsr & (UART_LSR_DR | UART_LSR_BI)))
+		return false;
+
+	if (!(port->status & (UPSTAT_AUTOCTS | UPSTAT_AUTORTS)))
+		return true;
+	if (lsr & (UART_LSR_FIFOE | UART_LSR_BRK_ERROR_BITS))
+		return true;
+	if (port->read_status_mask & UART_LSR_DR)
+		return true;
+
+	return false;
+}
+
+static int mxpcie8250_handle_irq(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	u16 lsr;
+	u8 iir;
+
+	iir = serial_in(up, UART_IIR);
+	if (iir & UART_IIR_NO_INT)
+		return 0;
+
+	guard(uart_port_lock_check_sysrq_irqsave)(port);
+
+	lsr = serial_lsr_in(up);
+	if (mxpcie8250_should_rx(up, lsr))
+		lsr = serial8250_rx_chars(up, lsr);
+
+	serial8250_modem_status(up);
+
+	if ((lsr & UART_LSR_THRE) && (up->ier & UART_IER_THRI))
+		serial8250_tx_chars(up);
+
+	return 1;
+}
+
 static void mxpcie8250_init_board(struct pci_dev *pdev, struct mxpcie8250 *priv)
 {
 	void __iomem *bar2_base = priv->bar2_base;
@@ -362,6 +403,7 @@ static int mxpcie8250_probe(struct pci_dev *pdev, const struct pci_device_id *id
 	up.port.shutdown = mxpcie8250_shutdown;
 	up.port.throttle = mxpcie8250_throttle;
 	up.port.unthrottle = mxpcie8250_unthrottle;
+	up.port.handle_irq = mxpcie8250_handle_irq;
 
 	for (unsigned int i = 0; i < num_ports; i++) {
 		mxpcie8250_setup_port(pdev, priv, &up, i);
-- 
2.45.2