Powering off modems

[Aleksander Morgado]

Hey,

I just merged some commits which enable ModemManager to tell the modem
to power-off completely (no new API, just allowing OFF in
SetPowerState()). The idea behind these changes is to let users of
ModemManager tell the modem to power-off before really cutting the
power source of the device. It is not a general use case (i.e. not
everyone should do that), only do it if you are able to cut the power
to the device and if you're about to do it after setting the modem in
OFF mode.

Currently it is implemented for QMI, Wavecom and Cinterion devices
only. For QMI devices, the device goes in OFFLINE mode, which can only
be recovered doing an actually physical power cycle (or with a RESET
command, which MM won't do automatically). For Cinterion devices, the
power off will make the ttys unusable (if RS232 device) or will really
remove the ttys (if USB device). For Wavecom devices, it ends up
removing the ttys and also rebooting the device after some seconds.

I was going to include CFUN=0 as default implementation, but didn't do
it. Maybe we should.

So, all in all, if you want to use the power off feature, make sure
you cut the power to the device as soon the SetPowerState(OFF) command
returns.

Cheers!

-- 
Aleksander
https://aleksander.es