From: Allen Yan <yanwei@marvell.com>
Date: Fri, 13 Oct 2017 11:01:53 +0200
Subject: serial: mvebu-uart: add TX interrupt trigger for pulse interrupts

Git-commit: 30434b0713a5f4ecf00e9ffd3d47053882b1909a
Patch-mainline: v4.15-rc1
References: fate#326470

Pulse interrupts (extended UART only) needs a change of state to trigger
the TX interrupt. In addition to enabling the TX_READY_INT_EN flag,
produce a FIFO state change from 'empty' to 'not full'. For this, write
only one data byte in TX start, making the TX FIFO not empty, and wait
for the TX interrupt to continue the transfer.

Signed-off-by: Allen Yan <yanwei@marvell.com>
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Reviewed-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
 drivers/tty/serial/mvebu-uart.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index 6bd0c40008bb..e52248ec2689 100644
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -165,8 +165,16 @@ static void mvebu_uart_stop_tx(struct uart_port *port)
 
 static void mvebu_uart_start_tx(struct uart_port *port)
 {
-	unsigned int ctl = readl(port->membase + UART_INTR(port));
+	unsigned int ctl;
+	struct circ_buf *xmit = &port->state->xmit;
 
+	if (IS_EXTENDED(port) && !uart_circ_empty(xmit)) {
+		writel(xmit->buf[xmit->tail], port->membase + UART_TSH(port));
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		port->icount.tx++;
+	}
+
+	ctl = readl(port->membase + UART_INTR(port));
 	ctl |= CTRL_TX_RDY_INT(port);
 	writel(ctl, port->membase + UART_INTR(port));
 }
-- 
2.11.0