Re: carl9170: not able to add P2P_GO - add_interface fail with -EBUSY

[Christian Lamparter <chunkeey@googlemail.com>]

On Friday 06 April 2012 17:11:29 Johannes Berg wrote:
> On Fri, 2012-04-06 at 13:22 +0200, Christian Lamparter wrote:
> 
> > > Is that chipset limitation we could add only new STA interface when
> > > main_vif is also STA?
> > <http://wireless.kernel.org/en/users/Drivers/carl9170#Multiple_Interfaces>
> > no, it's not. But you'll have to go through several hoops to extend
> > the driver to switch the "main" interface while the device is up and
> > running.
> 
> So the driver has a concept of the order in which interfaces are added?
> That's something I never considered when writing the interface type
> combinations support.
Actually, it's more of a master/slave situation. 

The MAC only has one security engine "mode" which can be either AP/IBSS/WDS.
[So, this setting will be shared with all virtual interfaces]
Next, the MAC only has one TSF counter, [beacon/tbtt timer, etc...] which
is also shared between the virtual interfaces [note: the TSF sync depends
on the mode as well, you see if the main interface is a station/ibss then
the TSF is automatically updated [by the hardware in fact] and there is
nothing a slave interface [e.g.: AP] can do!]. And then there is of
course the shared ERP, basic rates, slot time, multicast, QOS/WME, ... stuff.

Regards,
	Christian