Hi,
On Wed, 2022-01-19 at 16:11 +0100, Uwe Kleine-König wrote:
> On Wed, Jan 19, 2022 at 03:52:03PM +0100, Harald Seiler wrote:
> > Right now, even when `delay_rts_before_send` and `delay_rts_after_send`
> > are 0, the hrtimer is triggered (with timeout 0) which can introduce a
> > few 100us of additional overhead on slower i.MX platforms.
> >
> > Implement a fast path when the delays are 0, where the RTS signal is
> > toggled immediately instead of going through an hrtimer. This fast path
> > behaves identical to the code before delay support was implemented.
> >
> > Signed-off-by: Harald Seiler <hws@xxxxxxx>
> > ---
> > drivers/tty/serial/imx.c | 18 ++++++++++++++----
> > 1 file changed, 14 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> > index df8a0c8b8b29..67bbbb69229d 100644
> > --- a/drivers/tty/serial/imx.c
> > +++ b/drivers/tty/serial/imx.c
> > @@ -455,9 +455,14 @@ static void imx_uart_stop_tx(struct uart_port *port)
> > if (port->rs485.flags & SER_RS485_ENABLED) {
> > if (sport->tx_state == SEND) {
> > sport->tx_state = WAIT_AFTER_SEND;
> > - start_hrtimer_ms(&sport->trigger_stop_tx,
> > +
> > + if (port->rs485.delay_rts_after_send > 0) {
> > + start_hrtimer_ms(&sport->trigger_stop_tx,
> > port->rs485.delay_rts_after_send);
> > - return;
> > + return;
> > + }
> > +
> > + /* continue without any delay */
>
> Is it right to keep the assignment sport->tx_state = WAIT_AFTER_SEND ?
I am keeping the assignment intentionally, to fall into the
if(state == WAIT_AFTER_RTS) below (which then sets the state to OFF).
I originally had the code structured like this:
if (port->rs485.delay_rts_after_send > 0) {
sport->tx_state = WAIT_AFTER_SEND;
start_hrtimer_ms(&sport->trigger_stop_tx,
port->rs485.delay_rts_after_send);
return;
} else {
/* continue without any delay */
sport->tx_state = WAIT_AFTER_SEND;
}
This is functionally identical, but maybe a bit more explicit.
Not sure what is more clear to read?
> > }
> >
> > if (sport->tx_state == WAIT_AFTER_RTS ||
> > @@ -698,9 +703,14 @@ static void imx_uart_start_tx(struct uart_port *port)
> > imx_uart_stop_rx(port);
> >
> > sport->tx_state = WAIT_AFTER_RTS;
> > - start_hrtimer_ms(&sport->trigger_start_tx,
> > +
> > + if (port->rs485.delay_rts_before_send > 0) {
> > + start_hrtimer_ms(&sport->trigger_start_tx,
> > port->rs485.delay_rts_before_send);
> > - return;
> > + return;
> > + }
> > +
> > + /* continue without any delay */
>
> Here similar question here about sport->tx_state = WAIT_AFTER_RTS;
Same as above, but with WAIT_AFTER_RTS of course...
--
Harald
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