Subject: Re: New Regulatory Domain Api.
From: Marcel Holtmann <holtmann@linux.intel.com>
To: "Luis R. Rodriguez" <lrodriguez@atheros.com>
Cc: Johannes Berg <johannes@sipsolutions.net>,
	"John W. Linville" <linville@tuxdriver.com>,
	Zhu Yi <yi.zhu@intel.com>,
	"Kolekar, Abhijeet" <abhijeet.kolekar@intel.com>,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
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Date: Wed, 15 Oct 2008 19:47:48 +0200
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Hi Luis,

> > I can see it useful when companies actually start building products with
> > two or more cards in the system and have different cards for different
> > tasks in it. So if you stick one card for one band and another one for
> > the other band in there, then it would make sense to do a per-band
> > regulatory hinting.
> 
> Sure, but custom solutions can require custom regulatory dbs and
> people can do any crazy thing they want here, just as when they need
> custom regulatory domains not allowed by the FCC in the USA for
> example. Remember that by default the design is trying to cover the
> usual scenario of users with 1 wireless card or 2 with one built in.
> We decided on our discussions to respect the built-in card first. For
> more cards we can take the intersection if we want to keep being more
> restrictive. Its what makes sense if you think about it.

I must admit that I never thought about the implications of multiple
bands with multiple hardware. I am not against keeping it simple and
forcing to have userspace in place to change it. However we do wanna
have support for old laptops that are currently working fine with no
extra userspace, but newer kernels where they just add the second card
to access an A-network. Also remember that internal cards can't really
be disabled most of the times.

> > Not sure if this really ever ends up in a product. However I can see the
> > case where you have a laptop with a BG-card and then attach an A-card to
> > it do access an A-network and then it doesn't work. It would be nice to
> > just have this working. Currently this would not work.
> 
> Yes it does, it just doesn't work for your hardware as Intel put into
> regulatory hardware capability and these are two *very* different
> things. That is the problem.
> 
> My suggestion is to add a default minimal 5 GHz regulatory domain
> definition to your driver on single band cards to deal with this. When
> a dual band card is present then all of the full card's capabilities
> will be used.

That would be one option, but it sounds really strange to me that a
BG-card has to "think" about A-bands.

Let not try to put this down into the drivers if we can solve this
nicely with a per-band regulatory hints inside the core.

> > Also the case when we unplug the first card, does the regulatory hint
> > gets reset and the next card could bring in a new one? I can see use
> > cases where you don't wanna use the built-in card, because it is just
> > too limited.
> 
> For now nl80211 supports changing regulatory domains.

Please keep in mind the case where we do have a new kernel with old
userspace or an userspace without CRDA.

Regards

Marce