[PATCH 1/4] serial: 8250_dw: add em485 support

[Giulio Benetti]

Need to use rs485 transceiver so let's use existing em485 485 emulation
layer on top of 8250.

Add rs485_config callback to port.

Signed-off-by: Giulio Benetti <giulio.bene...@micronovasrl.com>
---
 drivers/tty/serial/8250/8250_dw.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_dw.c 
b/drivers/tty/serial/8250/8250_dw.c
index 6fcdb90f616a..45366e6e5411 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -314,6 +314,36 @@ static void dw8250_set_ldisc(struct uart_port *p, struct 
ktermios *termios)
        serial8250_do_set_ldisc(p, termios);
 }
 
+static int dw8250_rs485_config(struct uart_port *p,
+                              struct serial_rs485 *rs485)
+{
+       struct uart_8250_port *up = up_to_u8250p(p);
+
+       /* Clamp the delays to [0, 100ms] */
+       rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
+       rs485->delay_rts_after_send  = min(rs485->delay_rts_after_send, 100U);
+
+       p->rs485 = *rs485;
+
+       /*
+        * Both serial8250_em485_init and serial8250_em485_destroy
+        * are idempotent
+        */
+       if (rs485->flags & SER_RS485_ENABLED) {
+               int ret = serial8250_em485_init(up);
+
+               if (ret) {
+                       rs485->flags &= ~SER_RS485_ENABLED;
+                       p->rs485.flags &= ~SER_RS485_ENABLED;
+               }
+               return ret;
+       }
+
+       serial8250_em485_destroy(up);
+
+       return 0;
+}
+
 /*
  * dw8250_fallback_dma_filter will prevent the UART from getting just any free
  * channel on platforms that have DMA engines, but don't have any channels
@@ -449,6 +479,7 @@ static int dw8250_probe(struct platform_device *pdev)
        p->serial_out   = dw8250_serial_out;
        p->set_ldisc    = dw8250_set_ldisc;
        p->set_termios  = dw8250_set_termios;
+       p->rs485_config = dw8250_rs485_config;
 
        p->membase = devm_ioremap(dev, regs->start, resource_size(regs));
        if (!p->membase)
-- 
2.17.1