[PATCH next v2 1/4] serial: 8250: Split out IER from rs485_start_tx()

[John Ogness <john.ogness@xxxxxxxxxxxxx>]

Move IER handling out of rs485_start_tx() callback and into a new
wrapper serial8250_rs485_start_tx(). Replace all callback call sites
with wrapper, except for the console write() callback, where it is
inappropriate to modify IER.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
---
 drivers/tty/serial/8250/8250.h      |  2 ++
 drivers/tty/serial/8250/8250_port.c | 27 +++++++++++++++++++++------
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index e5310c65cf52..6e90223ba1d6 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -236,6 +236,8 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p);
 void serial8250_em485_destroy(struct uart_8250_port *p);
 extern struct serial_rs485 serial8250_em485_supported;
 
+void serial8250_rs485_start_tx(struct uart_8250_port *up);
+
 /* MCR <-> TIOCM conversion */
 static inline int serial8250_TIOCM_to_MCR(int tiocm)
 {
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 2786918aea98..ba8d9cefc451 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1370,7 +1370,6 @@ static void serial8250_stop_rx(struct uart_port *port)
 	serial8250_rpm_get(up);
 
 	up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
-	up->port.read_status_mask &= ~UART_LSR_DR;
 	serial_port_out(port, UART_IER, up->ier);
 
 	serial8250_rpm_put(up);
@@ -1543,16 +1542,20 @@ static inline void __start_tx(struct uart_port *port)
  *
  * Generic callback usable by 8250 uart drivers to start rs485 transmission.
  * Assumes that setting the RTS bit in the MCR register means RTS is high.
- * (Some chips use inverse semantics.)  Further assumes that reception is
- * stoppable by disabling the UART_IER_RDI interrupt.  (Some chips set the
- * UART_LSR_DR bit even when UART_IER_RDI is disabled, foiling this approach.)
+ * (Some chips use inverse semantics.)
+ * It does not disable RX interrupts. Use the wrapper function
+ * serial8250_rs485_start_tx() if that is also needed.
  */
 void serial8250_em485_start_tx(struct uart_8250_port *up)
 {
 	unsigned char mcr = serial8250_in_MCR(up);
 
+	/*
+	 * Some chips set the UART_LSR_DR bit even when UART_IER_RDI is
+	 * disabled, so explicitly mask it.
+	 */
 	if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
-		serial8250_stop_rx(&up->port);
+		up->port.read_status_mask &= ~UART_LSR_DR;
 
 	if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
 		mcr |= UART_MCR_RTS;
@@ -1562,6 +1565,18 @@ void serial8250_em485_start_tx(struct uart_8250_port *up)
 }
 EXPORT_SYMBOL_GPL(serial8250_em485_start_tx);
 
+/**
+ * serial8250_rs485_start_tx() - stop rs485 reception, enable transmission
+ * @up: uart 8250 port
+ */
+void serial8250_rs485_start_tx(struct uart_8250_port *up)
+{
+	if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+		serial8250_stop_rx(&up->port);
+
+	up->rs485_start_tx(up);
+}
+
 /* Returns false, if start_tx_timer was setup to defer TX start */
 static bool start_tx_rs485(struct uart_port *port)
 {
@@ -1585,7 +1600,7 @@ static bool start_tx_rs485(struct uart_port *port)
 	if (em485->tx_stopped) {
 		em485->tx_stopped = false;
 
-		up->rs485_start_tx(up);
+		serial8250_rs485_start_tx(up);
 
 		if (up->port.rs485.delay_rts_before_send > 0) {
 			em485->active_timer = &em485->start_tx_timer;
-- 
2.39.2