[PATCH v4 3/5] tty: serial: sh-sci: Fix Tx on SCI IP

[Biju Das <biju.das.jz@xxxxxxxxxxxxxx>]

For SCI, the TE (transmit enable) must be set after setting TIE (transmit
interrupt enable) or in the same instruction to start the transmission.
Set TE bit in sci_start_tx() instead of set_termios() for SCI and clear
TE bit, if circular buffer is empty in sci_transmit_chars().

Fixes: 93bcefd4c6ba ("serial: sh-sci: Fix setting SCSCR_TIE while transferring data")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
---
v3->v4:
 * Updated fixes tag.
v3:
 * New patch
---
 drivers/tty/serial/sh-sci.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 15954ca3e9dc..bcc4152ce043 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -596,6 +596,15 @@ static void sci_start_tx(struct uart_port *port)
 	if (!s->chan_tx || port->type == PORT_SCIFA || port->type == PORT_SCIFB) {
 		/* Set TIE (Transmit Interrupt Enable) bit in SCSCR */
 		ctrl = serial_port_in(port, SCSCR);
+
+		/*
+		 * For SCI, TE (transmit enable) must be set after setting TIE
+		 * (transmit interrupt enable) or in the same instruction to start
+		 * the transmit process.
+		 */
+		if (port->type == PORT_SCI)
+			ctrl |= SCSCR_TE;
+
 		serial_port_out(port, SCSCR, ctrl | SCSCR_TIE);
 	}
 }
@@ -834,6 +843,12 @@ static void sci_transmit_chars(struct uart_port *port)
 			c = xmit->buf[xmit->tail];
 			xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
 		} else {
+			if (port->type == PORT_SCI) {
+				ctrl = serial_port_in(port, SCSCR);
+				ctrl &= ~SCSCR_TE;
+				serial_port_out(port, SCSCR, ctrl);
+				return;
+			}
 			break;
 		}
 
@@ -2580,8 +2595,14 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios,
 		sci_set_mctrl(port, port->mctrl);
 	}
 
-	scr_val |= SCSCR_RE | SCSCR_TE |
-		   (s->cfg->scscr & ~(SCSCR_CKE1 | SCSCR_CKE0));
+	/*
+	 * For SCI, TE (transmit enable) must be set after setting TIE
+	 * (transmit interrupt enable) or in the same instruction to
+	 * start the transmitting process. So skip setting TE here for SCI.
+	 */
+	if (port->type != PORT_SCI)
+		scr_val |= SCSCR_TE;
+	scr_val |= SCSCR_RE | (s->cfg->scscr & ~(SCSCR_CKE1 | SCSCR_CKE0));
 	serial_port_out(port, SCSCR, scr_val | s->hscif_tot);
 	if ((srr + 1 == 5) &&
 	    (port->type == PORT_SCIFA || port->type == PORT_SCIFB)) {
-- 
2.25.1