Hi, * Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> [700101 02:00]: > 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. This patch seems to cause a runtime PM regression in v5.18-rc1 where 8250 is never idled for omaps. Looks like the return added here is not paired with put for the serial8250_rpm_get_tx() call above? Regards, Tony #regzbot ^introduced 932d596378b0 > 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 >
