linux-kernel - Re: [PATCH v6 3/3] tty: 8250_omap: Use software emulated RS485 direction control

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Message-ID: <56991F32.1030505@hurleysoftware.com>
Date:	Fri, 15 Jan 2016 08:32:50 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Matwey V. Kornilov" <matwey@....msu.ru>
Cc:	gregkh@...uxfoundation.org, jslaby@...e.com,
	andy.shevchenko@...il.com, gnomes@...rguk.ukuu.org.uk,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v6 3/3] tty: 8250_omap: Use software emulated RS485
 direction control

On 12/21/2015 10:26 AM, Matwey V. Kornilov wrote:
> Use software emulated RS485 direction control to provide RS485 API existed in
> omap_serial driver. Note that 8250_omap issues interrupt on shift register
> empty which is single prerequesite for using software emulated RS485.

Again, sorry for the long delay; comments below.

> Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
> ---
>  drivers/tty/serial/8250/8250_omap.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 826c5c4..323c0a4 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -698,6 +698,23 @@ static void omap_8250_throttle(struct uart_port *port)
>  	pm_runtime_put_autosuspend(port->dev);
>  }
>  
> +static int omap_8250_rs485_config(struct uart_port *port, struct serial_rs485 *rs485)
> +{
> +	struct uart_8250_port *up = up_to_u8250p(port);
> +
> +	if (rs485->flags & SER_RS485_ENABLED && !serial8250_em485_enabled(up)) {
> +		port->rs485 = *rs485;

Please clamp the delay values to something reasonable; 100ms?

> +		return serial8250_em485_init(up);
> +	}
> +
> +	if (serial8250_em485_enabled(up) && !(rs485->flags & SER_RS485_ENABLED))
> +		serial8250_em485_destroy(up);
> +
> +	port->rs485 = *rs485;

This logic seems a little convoluted; you're checking the state here but
then you're re-checking the state in init/destroy.

Regards,
Peter Hurley

> +
> +	return 0;
> +}
> +
>  static void omap_8250_unthrottle(struct uart_port *port)
>  {
>  	unsigned long flags;
> @@ -1144,6 +1161,7 @@ static int omap8250_probe(struct platform_device *pdev)
>  	up.port.shutdown = omap_8250_shutdown;
>  	up.port.throttle = omap_8250_throttle;
>  	up.port.unthrottle = omap_8250_unthrottle;
> +	up.port.rs485_config = omap_8250_rs485_config;
>  
>  	if (pdev->dev.of_node) {
>  		const struct of_device_id *id;
>