From: Marek Vasut <marex@xxxxxxx>
[ Upstream commit c47527cbcc3c50800f34b8c684f29721f75de246 ]
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>
Link: https://lore.kernel.org/r/20230223042252.95480-2-marex@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 409e91d6829a5..81a53cc41dcb8 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -689,8 +689,9 @@ 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);
}
--
2.39.2
