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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20151117092442.GL22022@pengutronix.de>
Date:	Tue, 17 Nov 2015 10:24:42 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	"Matwey V. Kornilov" <matwey@....msu.ru>
Cc:	gregkh@...uxfoundation.org, jslaby@...e.com,
	peter@...leysoftware.com, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 5/5] tty: Add software emulated RS485 support for 8250

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

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/