Re: [PATCH v3 5/5] tty: Add software emulated RS485 support for 8250

Uwe Kleine-König
2015-11-17T09:24:55Z

Hello,

On Thu, Nov 12, 2015 at 05:33:56PM +0300, Matwey V. Kornilov wrote:
> +static void serial8250_start_tx(struct uart_port *port)
> +{
> + struct uart_8250_port *up = up_to_u8250p(port);
> + __u32 delay;
> +
> + serial8250_rpm_get_tx(up);
> +
> + if (timer_pending(&up->rs485_start_tx_timer))
> + return;

I think this is wrong (or at least suboptimal). The .start_tx callback
can be called even if transmission is already ongoing. In this case you
don't want to restart the rs485_start_tx_timer.

> + if ((delay = serial8250_rs485_start_tx(up))) {
> + mod_timer(&up->rs485_start_tx_timer, jiffies + delay * HZ / 1000);
> + } else {
> + __start_tx(port);
> + }
> +}
> +
> [...]
> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index faa0e03..c4905e7 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -86,6 +86,8 @@ struct uart_8250_ops {
> struct uart_8250_port {
> struct uart_port port;
> struct timer_list timer; /* "no irq" timer */
> + struct timer_list rs485_start_tx_timer; /* "rs485 start tx" timer */
> + struct timer_list rs485_stop_tx_timer; /* "rs485 stop tx" timer */

Do you really need two timers here? At each point in time there should
only be at most one of them active.

Best regards
Uwe

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