linux-kernel - Re: should RTS init in serial core be tied to CRTSCTS

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Message-ID: <20070305083918.GA26436@flint.arm.linux.org.uk>
Date:	Mon, 5 Mar 2007 08:39:18 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Robin Getz <rgetz@...ckfin.uclinux.org>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org
Subject: Re: should RTS init in serial core be tied to CRTSCTS

On Sun, Mar 04, 2007 at 03:42:25PM -0500, Robin Getz wrote:
> On Sun 4 Mar 2007 14:46, Russell King pondered:
> > On Thu, Mar 01, 2007 at 07:03:02PM -0500, Mike Frysinger wrote:
> >  > the console= bootcmd allows for controlling of the initial state of
> >  > flow control by adding/omitting the 'r' suffix ...
> >
> >  The console command *only* sets the state for the kernel's use of one
> >  serial port.  It does not affect any other serial port, so tying
> >  random RTS behaviours into that command line option is absolutely
> >  silly.
> 
> I have one serial port in the system, it shares console, and the 
> communications port for the application. (But I guess that is besides the 
> point).

In which case communications over that port could be unreliable.
What if the kernel decides to spit out a message in the middle of
your applications data transfer?

If you're using a serial port for a data application, don't make it
the kernel console.

> When the common serial core initialises the UART, and sees that it has the 
> capability to do HW flow control - it enables it, asserting the pin, even if 
> I don't want it at that moment in time.
> 
> The real issue is that there is some legacy equipment, which gets confused if 
> it sees glitches on RTS (which happens today, when serial core init asserts 
> RTS, and then the the main application turns it off)...
> 
> How do I set the set up the UART, so RTS is avaliable, but not enabled?

No idea, sorry.  It's not something any Linux kernel version has ever
supported, and since I no longer do serial support it's not something
I'd be involved with anymore.

All I will say is that thinking about keying such a decision off the
kernel console= parameter is absolutely silly - the console= parameter
has nothing to do with the serial port's userspace settings.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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