linux-kernel - Re: [PATCH v8 3/3] tty: 8250_omap: Use software emulated RS485 direction control

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Date:	Thu, 11 Feb 2016 19:40:14 +0300
From:	Ильяс Гасанов 
	<torso.nafi@...il.com>
To:	"Matwey V. Kornilov" <matwey@....msu.ru>
Cc:	gregkh@...uxfoundation.org, jslaby@...e.com,
	Peter Hurley <peter@...leysoftware.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	gnomes@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v8 3/3] tty: 8250_omap: Use software emulated RS485
 direction control

Hello,

2016-02-01 21:09 GMT+03:00 "Matwey V. Kornilov" <matwey@....msu.ru>:
> +static int omap_8250_rs485_config(struct uart_port *port,
> +                                 struct serial_rs485 *rs485)
> +{
> +       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);
> +
> +       port->rs485 = *rs485;
> +
> +       /*
> +        * Both serial8250_em485_init and serial8250_em485_destroy
> +        * are idempotent
> +        */
> +       if (rs485->flags & SER_RS485_ENABLED) {
> +               int ret = serial8250_em485_init(up);
> +
> +               if (ret) {
> +                       rs485->flags &= ~SER_RS485_ENABLED;
> +                       port->rs485.flags &= ~SER_RS485_ENABLED;
> +               }
> +               return ret;
> +       }
> +
> +       serial8250_em485_destroy(up);
> +
> +       return 0;
> +}

I think that an invocation of serial8250_em485_destroy() should be
performed inside omap8250_remove() as well. However there is a catch -
serial8250_get_port() is only reserved for suspend-resume power
management operations, and I am aware of no other means how to supply
an uart_8250_port to serial8250_em485_destroy() at that point.

Similarly, I got no idea on how to implement handling
"linux,rs485-enabled-at-boot-time" property without using
serial8250_get_port() directly (well, honestly I could try invoking
the corresponding ioctl somehow, but that's gonna be plain ugly at
least).

Regards,
Ilyas G.