The stm32_usart_transmit_chars() may be called with empty or stopped
transmit queue, and no XON/OFF character pending. This can happen at
the end of transmission, where this last call is used to either handle
the XON/XOFF x_char, or disable TX interrupt if queue is empty or
stopped.
If that occurs, do not assert the RS485 RTS/DE GPIO anymore, as the
GPIO would remain asserted past the end of transmission and that would
block the RS485 bus after the transmission.
Only assert the RS485 RTS/DE GPIO if there is either pending XON/XOFF
x_char, or at least one character in running transmit queue.
Fixes: d7c76716169d ("serial: stm32: Use TC interrupt to deassert GPIO RTS in RS485 mode")
Signed-off-by: Marek Vasut <marex@xxxxxxx>
---
Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
Cc: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jean Philippe Romain <jean-philippe.romain@xxxxxxxxxxx>
Cc: Jiri Slaby <jirislaby@xxxxxxxxxx>
Cc: Johan Hovold <johan@xxxxxxxxxx>
Cc: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
Cc: Valentin Caron <valentin.caron@xxxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-serial@xxxxxxxxxxxxxxx
Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
drivers/tty/serial/stm32-usart.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index bf51e2152dd5a..1e38fc9b10c11 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -693,8 +693,9 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
int ret;
if (!stm32_port->hw_flow_control &&
- port->rs485.flags & SER_RS485_ENABLED) {
- stm32_port->txdone = false;
+ port->rs485.flags & SER_RS485_ENABLED &&
+ (port->x_char ||
+ !(uart_circ_empty(xmit) || uart_tx_stopped(port)))) {
stm32_usart_tc_interrupt_disable(port);
stm32_usart_rs485_rts_enable(port);
}
--
2.39.1
