linux-kernel - RE: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

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Message-ID: <000f01c8f88c$ad29d950$2e01a8c0@acksys.local>
Date:	Thu, 7 Aug 2008 14:54:05 +0200
From:	"Tosoni" <jp.tosoni@...sys.fr>
To:	"'Laurent Pinchart'" <laurentp@...-semaphore.com>,
	"'Aristeu Rozanski'" <arozansk@...hat.com>
Cc:	<linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

In my opinion, DSR/DTR is another (wrong) way to do RTS/CTS flow control, so
I would have it implemented in setserial as a modifier to the CRTSCTS flag.

About a RS485 ioctl: could you consider the attached files which are already
in the Linux kernel (in include/asm-cris).
They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
with allows to specify timings. Sounds just like what we want ?

JP Tosoni

> -----Original Message-----
> From: linux-serial-owner@...r.kernel.org
> [mailto:linux-serial-owner@...r.kernel.org]On Behalf Of
> Laurent Pinchart
> Sent: Thursday, August 07, 2008 10:32 AM
> To: Aristeu Rozanski
> Cc: linux-serial@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow
> control
>
>
> Hi,
>
> On Wednesday 06 August 2008, Aristeu Rozanski wrote:
> > This patch adds support for DTR/DSR hardware flow control
> on 8250 driver on
> > x86 machines. It's done by adding a CDTRDSR flag to work
> just like CRTSCTS,
> > which is not done on other architectures on purpose (so
> each maintainer can
> > allocate it).
>
> It's funny, serial flow control hasn't been discussed for a
> long time, and you're the third person to start a flow
> control related thread on this mailing list in a few days.
>
> > This patch was tested with success with a serial printer
> configured with a
> > small buffer and DTR/DSR flow control.
> >
> > This is based on the work of Michael Westermann
> > (http://lkml.org/lkml/2007/8/31/133)
> >
> > Comments more than welcome.
>
> Please read the '[PATCH/RFC] 8250: Auto RS485 direction
> control' thread for background information. In a nutshell we
> need more than just CTS/RTS and DTR/DSR, and we don't have
> enough c_cflags bits. We will probably have to create a new ioctl.
>
> Best regards,
>
> --
> Laurent Pinchart
> CSE Semaphore Belgium
>
> Chaussee de Bruxelles, 732A
> B-1410 Waterloo
> Belgium
>
> T +32 (2) 387 42 59
> F +32 (2) 387 42 75
>

View attachment "ioctls.h" of type "text/plain" (2864 bytes)

View attachment "rs485.h" of type "text/plain" (455 bytes)