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

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Message-ID: <20070308204020.GE30023@flint.arm.linux.org.uk>
Date:	Thu, 8 Mar 2007 20:40:21 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Robin Getz <rgetz@...ckfin.uclinux.org>
Cc:	Oleksiy Kebkal <kebkal@...il.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	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 Thu, Mar 08, 2007 at 03:23:39PM -0500, Robin Getz wrote:
> On Thu 8 Mar 2007 08:48, Russell King pondered:
> > On Thu, Mar 08, 2007 at 08:44:31AM -0500, Robin Getz wrote:
> > > That would let you change things are run time, but the problem is at
> > > boot time. A default setting needs to be set, so when things initialize,
> > > and proc does not exist yet, it is still set properly...
> >
> > I disagree.  "proc does not exist yet" - the only time that applies is
> > long before userspace as active.
> 
> Right - We both agree - And setting console=/dev/null in the bootargs still 
> does not help.

Ok, good.

> When the kernel initializes the UART Port, it asserts RTS - which confuses
> the host it is attached to (in this case, the Linux system is the serial 
> peripheral).

... which occurs /after/ userspace is up and running, when sysfs is
available.  So putting it in sysfs is reasonable.

> How about adding a module_param to serial core, which the default is to
> assert RTS (as is today), and someone (like me) can override with
> serial_core.RTS=0

So all ports change behaviour with a single parameter?  That'll stop
NULL modem cables with hardware flow control enabled working on other
ports without compensatory tweaking.

No, doing a system-wide change like that is _not_ a solution - it just
moves the problem elsewhere.

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