serial: 8250: handle DTR in rs485 emulation
From: Heiko Stuebner <heiko.stuebner@...> Date: Thu, 12 Mar 2020 15:15:13 +0100
Commit-Message
While in a lot of cases only RTS is needed as DE signal, sometimes the RE signals is to be controlled separately, as DTR pin. So add necessary control functions for it. Signed-off-by: Heiko Stuebner <heiko.stuebner@...>
Patch-Comment
drivers/tty/serial/8250/8250_port.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
Statistics
- 13 lines added
- 0 lines removed
Changes
--------------------- drivers/tty/serial/8250/8250_port.c ----------------------
index 3d1d8490bc42..f8e5c096ed51 100644
@@ -572,6 +572,10 @@ static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
mcr &= ~UART_MCR_RTS;
p->port.mctrl &= ~TIOCM_RTS;
}
+
+ mcr |= UART_MCR_DTR;
+ p->port.mctrl |= TIOCM_DTR;
+
serial8250_out_MCR(p, mcr);
}
@@ -1558,6 +1562,13 @@ static inline void start_tx_rs485(struct uart_port *port)
em485->active_timer = NULL;
mcr = serial8250_in_MCR(up);
+
+ /* in rx_during_tx mode keep DTR active, to receive data */
+ if (up->port.rs485.flags & SER_RS485_RX_DURING_TX)
+ mcr |= UART_MCR_DTR;
+ else
+ mcr &= ~UART_MCR_DTR;
+
if (!!(up->port.rs485.flags & SER_RS485_RTS_ON_SEND) !=
!!(mcr & UART_MCR_RTS)) {
if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
@@ -1572,6 +1583,8 @@ static inline void start_tx_rs485(struct uart_port *port)
up->port.rs485.delay_rts_before_send);
return;
}
+ } else {
+ serial8250_out_MCR(up, mcr);
}
__start_tx(port);