linux-kernel - Linux 2.6.x - Serial port signalling not maintained when closing device

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Date:	Thu, 26 Mar 2009 08:42:20 +0100
From:	Paul Rolland <rol@...917.net>
To:	linux-kernel@...r.kernel.org
Cc:	rol@...917.net
Subject: Linux 2.6.x - Serial port signalling not maintained when closing
 device

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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