From: Marek Vasut marex@denx.de
[ 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@denx.de Link: https://lore.kernel.org/r/20230223042252.95480-2-marex@denx.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 0e8158cfaf0f9..3b7d4481edbea 100644 --- a/drivers/tty/serial/stm32-usart.c +++ b/drivers/tty/serial/stm32-usart.c @@ -502,8 +502,9 @@ 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); }