linux-kernel - Re: [PATCH v2 4/9] serial: 8250: add support for rs485 RTS delays in microseconds

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Date:   Fri, 29 Mar 2019 15:36:33 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Martin Kepplinger <martin.kepplinger@...zinger.com>,
        gregkh@...uxfoundation.org, robh+dt@...nel.org,
        mark.rutland@....com, jslaby@...e.com, corbet@....net,
        richard.genoud@...il.com, nicolas.ferre@...rochip.com,
        alexandre.belloni@...tlin.com, ludovic.desroches@...rochip.com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com
Cc:     linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH v2 4/9] serial: 8250: add support for rs485 RTS delays in
 microseconds

On 21/2/19 18:17, Martin Kepplinger wrote:
> Read struct serial_rs485's flag SER_RS485_DELAY_IN_USEC and apply the delay
> accordingly.
> 
> Signed-off-by: Martin Kepplinger <martin.kepplinger@...zinger.com>
> ---
>  drivers/tty/serial/8250/8250_omap.c | 13 +++++++++++--
>  drivers/tty/serial/8250/8250_port.c | 25 +++++++++++++++++++++----
>  2 files changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 0a8316632d75..cbce43ac60b1 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -720,8 +720,17 @@ static int omap_8250_rs485_config(struct uart_port *port,
>  	struct uart_8250_port *up = up_to_u8250p(port);
>  
>  	/* Clamp the delays to [0, 100ms] */
> -	rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
> -	rs485->delay_rts_after_send  = min(rs485->delay_rts_after_send, 100U);
> +	if (rs485->flags & SER_RS485_DELAY_IN_USEC) {
> +		rs485->delay_rts_before_send = min(rs485->delay_rts_before_send,
> +						   100000U);
> +		rs485->delay_rts_after_send  = min(rs485->delay_rts_after_send,
> +						   100000U);
> +	} else {
> +		rs485->delay_rts_before_send = min(rs485->delay_rts_before_send,
> +						   100U);
> +		rs485->delay_rts_after_send  = min(rs485->delay_rts_after_send,
> +						   100U);
> +	}
>  
>  	port->rs485 = *rs485;
>  
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index d2f3310abe54..0cee4aa8323d 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1483,6 +1483,15 @@ static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
>  	hrtimer_start(hrt, t, HRTIMER_MODE_REL);
>  }
>  
> +static void start_hrtimer_us(struct hrtimer *hrt, unsigned long usec)
> +{
> +	long sec = usec / 1000000;
> +	long nsec = (usec % 1000000) * 1000000000;

This 1e9 should be 1000 ("NSEC_PER_USEC").
While at it you might want to use USEC_PER_SEC (and MSEC_PER_SEC
above) to make the code more readable.

Cheers
Ahmad

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