Date: Thu, 26 Mar 2009 08:42:20 +0100
From: Paul Rolland <rol@as2917.net>
To: linux-kernel@vger.kernel.org
Cc: rol@as2917.net
Subject: Linux 2.6.x - Serial port signalling not maintained when closing
 device
Message-ID: <20090326084220.4def5652@tux.DEF.witbe.net>
Organization: AS2917.net
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Hello,

I'm using small devices that are connected on the serial port, and powered
using RTS and DTR.
When using kernel 2.4.x (at least 2.4.31), I could easily control the
powering of the device using :
 stty -F /dev/ttyS0 ospeed 9600 (this would put RTS and DTR to 1 / power)
and
 stty -F /dev/ttyS0 ospeed 0 (this would turn it off).

I've recently updated one of the machine to a new 2.6.29 kernel, and this
is not working anymore.
As far as I can see, I need to have an application that keeps /dev/ttyS0
open for this to work. As soon as no application is using the port,
everything goes down again.

This is a significant change between 2.4.x and 2.6.x. Is there a way to
change 2.6.x behavior to go back to the 2.4.x ? When was this change
introduce ?

This serial port controler is a 16550A, the machine is an x86 platform, so
nothing unusual.

Best regards,
Paul
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