netdev - Re: Network drivers that don't suspend on interface down

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Message-Id: <1166670411.23168.13.camel@localhost.localdomain>
Date:	Wed, 20 Dec 2006 22:06:51 -0500
From:	Dan Williams <dcbw@...hat.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Jiri Benc <jbenc@...e.cz>, Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Network drivers that don't suspend on interface down

On Thu, 2006-12-21 at 01:15 +0000, Matthew Garrett wrote:
> On Wed, Dec 20, 2006 at 01:12:51PM -0500, Dan Williams wrote:
> 
> > Entirely correct.  If the card is DOWN, the radio should be off (both TX
> > & RX) and it should be in max power save mode.  If userspace expects to
> > be able to get the card to do _anything_ when it's down, that's just
> > 110% wrong.  You can't get link events for many wired cards when they
> > are down, so I fail to see where userspace could expect to do anything
> > with a wireless card when it's down too.
> 
> Because it works on the common hardware? If there's documentation about 
> what userspace can legitimately expect, then I'm happy to defer to that. 
> But in the absence of any indication as to what functionality users can 
> depend on, deciding that existing functionality is a bug is, well, 
> impolite.
> 
> > Also, how does rfkill fit into this?  rfkill implies killing TX, but do
> > we have the granularity to still receive while the transmit paths are
> > powered down?
> 
> Is rfkill not just primarily an interface for us getting events when the 
> radio changes state? Every time I read up on it I get a little more 
> confused - some time I really need to make sense of it...

That's OK, it's really complicated.  There are 3 cases of rfkill
switches AFAICT:

a) tied to the wireless hardware, switch kills hardware directly
b) tied to wireless hardware, but driver handles the kill request
c) just another key, a separate key driver handles the event and asks
the wireless driver to kill the card

It's also complicated because some switches are supposed to rfkill both
an 802.11 module _and_ a bluetooth module at the same time, or I guess
some laptops may even have one rfkill switch for each wireless device.
Furthermore, some people want to 'softkill' the hardware via software
without pushing the key, which is a subset of (b) or (c) above.

It sucks.  But we _need_ a unified interface to handle it.

Dan


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