Re: nmcli radio off connected to ModemManager power state low

[Dan Williams <dcbw redhat com>]

On Fri, 2016-03-11 at 14:49 +0100, Carlo Lobrano wrote:
> Hello everybody,
>
> making some changes in ModemManager "set power state", I observed
> that setting
> setting a radio interface to OFF with nmcli, the ModemManager power
> state
> triggered is the LOW one, while I expected it to be the OFF one. Is
> that
> correct? If that so, is there a way to set the modem in OFF power
> state
> through network manager?

There are two things that 'nmcli r wwan off' does:

1) attempts to set any kernel rfkill WWAN switches to "blocked"
2) disables the modem with ModemManager, which sets low power state

If your kernel/hardware has rfkill capability then the modem will
actually be completely killed and off, and will often drop off the USB
bus too.

But if your kernel/hardware doesn't have rfkill, NM skips the rfkill
step and asks ModemManager to put the modem into low-power mode.
 Without rfkill capability if the modem/phone powers off completely
(which some do with CFUN=0), there's no way to get the modem turned
back on with 'nmcli r wwan on' because the modem has either completely
disappeared, or isn't responding to commands (because it's off).

So I looked through my collection and out of the 20 USB modems I tried,
only two actually powered off with CFUN=0; Nokia 21M-02 and Ericsson
MD300.  The rest stayed up and running, so obviously it would be
possible to use CFUN=0 (or equivalent) on most devices.

But is there a huge power draw difference between CFUN=0 and CFUN=4 in
most devices?  If there isn't, I'd prefer CFUN=4, and typically an
rfkill-setup is more useful for complete power off than CFUN=0 since
that also kills any USB power draw too.

Dan