From: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> Don't start the whole chain for TX if there is no data to send. This is mostly relevant for rs485 mode as there might be rts-before-send and rts-after-send delays involved. Signed-off-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> --- Hello, a few other drivers have such an early exit already (imx, stm32-usart). I wonder if it applies to all UART drivers that there is nothing to do in .start_tx() if the circ buffer is empty and there is no x_char to send. In this case it would be more sensible to ensure in serial_core that .start_tx() is only ever called if there is something to do. Best regards Uwe drivers/tty/serial/8250/8250_port.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 3b12bfc1ed67..5d4668f12f71 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1657,6 +1657,9 @@ static void serial8250_start_tx(struct uart_port *port) serial8250_rpm_get_tx(up); + if (!port->x_char && uart_circ_empty(&port->state->xmit)) + return; + if (em485 && em485->active_timer == &em485->start_tx_timer) return; base-commit: 754e0b0e35608ed5206d6a67a791563c631cec07 -- 2.34.1
