[PATCH 3/4] serial: sh-sci: Skip TDxE status clear for PORT_SCI

[Biju]

From: Au Dang <au.dang.jx@xxxxxxxxxxx>

On PORT_SCI, the TDxE (Transmit Data Empty) flag in SCxSR is cleared
automatically by hardware when data is written to TDR. Clearing it
again from software via clear_SCxSR() generates a spurious TXI
interrupt, which causes the last character to be transmitted twice.

Skip the clear_SCxSR() call for PORT_SCI in sci_transmit_chars() and
sci_poll_put_char(), as the hardware already handles it after each TDR
write.

Signed-off-by: Au Dang <au.dang.jx@xxxxxxxxxxx>
Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
---
 drivers/tty/serial/sh-sci.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index d577f9de6259..e4c7a3e14688 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -913,7 +913,8 @@ static void sci_poll_put_char(struct uart_port *port, unsigned char c)
 	} while (!(status & SCxSR_TDxE(port)));
 
 	sci_serial_out(port, SCxTDR, c);
-	s->ops->clear_SCxSR(port, SCxSR_TDxE_CLEAR(port) & ~SCxSR_TEND(port));
+	if (s->type != PORT_SCI)
+		s->ops->clear_SCxSR(port, SCxSR_TDxE_CLEAR(port) & ~SCxSR_TEND(port));
 }
 #endif /* CONFIG_CONSOLE_POLL || CONFIG_SERIAL_SH_SCI_CONSOLE ||
 	  CONFIG_SERIAL_SH_SCI_EARLYCON */
@@ -1049,7 +1050,8 @@ static void sci_transmit_chars(struct uart_port *port)
 		port->icount.tx++;
 	} while (--count > 0);
 
-	s->ops->clear_SCxSR(port, SCxSR_TDxE_CLEAR(port));
+	if (s->type != PORT_SCI)
+		s->ops->clear_SCxSR(port, SCxSR_TDxE_CLEAR(port));
 
 	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
-- 
2.43.0