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

[Biju Das <biju.das.jz@bp.renesas.com>]

As per the RZ/G2L users hardware manual (Rev.1.20 Sep, 2022), section
23.3.7 Serial Data Transmission (Asynchronous Mode) it is mentioned
that the TE (transmit enable) must be set after setting TIE (transmit
interrupt enable) or these 2 bits are set to 1 simultaneously by a
single instruction. So set these 2 bits in single instruction.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
---
v4:
 * Removed fixes tag.
v3:
 * New patch moved here from Renesas SCI fixes patch series
 * Updated commit description
 * Moved handling of clearing TE bit as separate patch#5.
---
 drivers/tty/serial/sh-sci.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 15743c2f3d3d..32f5c1f7d697 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -601,6 +601,15 @@ static void sci_start_tx(struct uart_port *port)
 	    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);
 	}
 }
@@ -2600,8 +2609,14 @@ 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