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Subject[PATCH 4/4] serial: 8250_dw: treat rpm suspend with -EBUSY if RS485 ON and RTS_AFTER_SEND
If rs485 is on and RTS_AFTER_SEND it means that in idle state rts pin
must be asserted, othwerwise rs485 transceiver will enter tx state.
dw8250 when clocks are stopped keeps rts line de-asserted(high),
resulting in keeping rs485 transceiver in tx state when port is idle.

Check if rs485 is on with RTS_AFTER_SEND set, if so return -EBUSY in

Signed-off-by: Giulio Benetti <>
drivers/tty/serial/8250/8250_dw.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 888280ff5451..6b0ee6dc8ad0 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -668,6 +668,11 @@ static int dw8250_resume(struct device *dev)
static int dw8250_runtime_suspend(struct device *dev)
struct dw8250_data *data = dev_get_drvdata(dev);
+ struct uart_8250_port *up = serial8250_get_port(data->line);
+ struct uart_port *p = &up->port;
+ if (p->rs485.flags & (SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND))
+ return -EBUSY;

if (!IS_ERR(data->clk))
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