On Thu, Oct 04, 2018 at 09:23:16AM +0200, Uwe Kleine-König wrote:
> serial8250_tx_chars() is called from several places and the callers don't
> consider that sending might not be allowed yet because the
> rts_before_send delay isn't over yet.
>
> So teach serial8250_tx_chars() about rts_before_send and delay the
> request accordingly if required.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> ---
> Cc: Tomas Melin <tomas.melin@xxxxxxxxxxx>
> Cc: Daniel Golle <daniel@xxxxxxxxxxxxxx>
> Cc: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
> Cc: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: Aaron Sierra <asierra@xxxxxxxxxxx>
> Cc: Rafael Gago <rafael.gago@xxxxxxxxx>
> Cc: Daniel Jedrychowski <avistel@xxxxxxxxx>
>
> Hello,
>
> on a powerpc (MPC8313) this patch prevents sending characters too early
> after an edge on CTS is detected. As the 8250 driver is quite "advanced"
> I'd welcome testing feedback for other chip variants, so I added a few
> people to Cc who did rs485 stuff in the past.
You pretty much missed the author of contribution of RS485 emulation
to 8250 driver.
Cc'ed to Matwey.
>
> drivers/tty/serial/8250/8250_port.c | 31 +++++++++++++++++++++++++++--
> 1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 3f779d25ec0c..d8d7456f8ec3 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1548,6 +1548,8 @@ static void serial8250_stop_tx(struct uart_port *port)
> serial8250_rpm_put(up);
> }
>
> +static void __serial8250_tx_chars(struct uart_8250_port *up);
> +
> static inline void __start_tx(struct uart_port *port)
> {
> struct uart_8250_port *up = up_to_u8250p(port);
> @@ -1565,7 +1567,7 @@ static inline void __start_tx(struct uart_port *port)
> lsr = serial_in(up, UART_LSR);
> up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
> if (lsr & UART_LSR_THRE)
> - serial8250_tx_chars(up);
> + __serial8250_tx_chars(up);
> }
> }
>
> @@ -1765,7 +1767,7 @@ unsigned char serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr)
> }
> EXPORT_SYMBOL_GPL(serial8250_rx_chars);
>
> -void serial8250_tx_chars(struct uart_8250_port *up)
> +static void __serial8250_tx_chars(struct uart_8250_port *up)
> {
> struct uart_port *port = &up->port;
> struct circ_buf *xmit = &port->state->xmit;
> @@ -1813,6 +1815,31 @@ void serial8250_tx_chars(struct uart_8250_port *up)
> if (uart_circ_empty(xmit) && !(up->capabilities & UART_CAP_RPM))
> __stop_tx(up);
> }
> +
> +/* called with port->lock taken and irqs off */
> +void serial8250_tx_chars(struct uart_8250_port *up)
> +{
> + struct uart_8250_em485 *em485;
> +
> + em485 = up->em485;
> + if (em485) {
> + if (em485->active_timer == &em485->start_tx_timer)
> + /*
> + * Still waiting for rts_before_send delay. When the
> + * timer triggers it will start tx.
> + */
> + return;
> +
> + /*
> + * tx might have finshed before and the driver waits for
> + * rts_after_send. Now as there is new data to be sent this
> + * is void.
> + */
> + em485->active_timer = NULL;
> + }
> +
> + __serial8250_tx_chars(up);
> +}
> EXPORT_SYMBOL_GPL(serial8250_tx_chars);
>
> /* Caller holds uart port lock */
> --
> 2.19.0
>
--
With Best Regards,
Andy Shevchenko
