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Date: Tue, 9 Aug 2016 10:14:29 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Ajay Garg <ajaygargnsit@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: Is it ok if ModemManager process is killed AFTER
 network-interface is brought up and IP-Address assigned?
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On Tue, Aug 09, 2016 at 12:48:12PM +0530, Ajay Garg wrote:
> Hi All.
> 
> We are using Sierra's USB-to-WWAN driver on Ubuntu-14 for Sierra's
> MC8090 modem, and we have a requirement wherein we need to have access
> to the modem-serial-port (from our user-application that is).
> 
> Right now, we see that /usr/sbin/ModemManager is always connected to
> /dev/ttyUSB3 (which means we cannot connect to the port from our
> application at the same time, or even if we can, received-data will be
> at best inconsistent).
> 
> 
> We are thinking of the following ::
> 
> * Initially, let nmcli and ModemManager do their work, and let them
> bring the WWAN interface up.
> 
> * Once this happens, we permanently-down the ModemManager from our
> application-binary, thereby freeing up /dev/ttyUSB3.
> 
> * Thereafter, we are free to connect to /dev/ttyUSB3 from our
> application, thereby using features like SMS-notification (+CMTI),
> signal-strength (+CSQ), etc.
> 
> 
> 
> Does our approach make sense?
> We will be grateful to any help.

Why not ask the modem manager team about this?  The kernel doesn't care
what you do with the device links :)

thanks,

greg k-h