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

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Message-ID: <20070309085753.GC29959@flint.arm.linux.org.uk>
Date:	Fri, 9 Mar 2007 08:57:53 +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 06:32:29PM -0500, Robin Getz wrote:
> On Thu 8 Mar 2007 15:40, Russell King pondered:
> > On Thu, Mar 08, 2007 at 03:23:39PM -0500, Robin Getz wrote:
> > > 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.
> 
> Hmm - maybe I don't understand things then.
> 
> Today - RTS gets asserted when serial_core calls uart_startup(), which is 
> pretty early in the boot process (unless it is loaded as a module - which I'm 
> not doing).

uart_startup() is called when something opens a serial port.  There's
two points which that happens:

1. when you have serial console enabled, and the kernel opens /dev/console
   before starting userspace.

2. when userspace opens a serial port.

If you're not using a serial console (and you don't have an utterly broken
/dev nodes - iow incorrect /dev/console entry), then (1) doesn't apply.

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