From: Michael Wu <flamingice@sourmilk.net>
To: "John W. Linville" <linville@tuxdriver.com>
Subject: Re: [PATCH 09/13] mac80211: remove hw_scan callback
Date: Wed, 25 Apr 2007 16:34:11 -0400
Cc: James Ketrenos <jketreno@linux.intel.com>,
	Jiri Benc <jbenc@suse.cz>, linux-wireless@vger.kernel.org
References: <20070423184811.7029.24949.stgit@magic.sourmilk.net> <462EE107.8040005@linux.intel.com> <20070425181656.GD5875@tuxdriver.com>
In-Reply-To: <20070425181656.GD5875@tuxdriver.com>
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On Wednesday 25 April 2007 14:16, John W. Linville wrote:
> On Tue, Apr 24, 2007 at 10:03:03PM -0700, James Ketrenos wrote:
> > (I would like to see hw_scan remain since iwlwifi uses it -- which we
> > hope to submit as soon as the code restructuring is complete)
>
> I was going to mention this in response to Michael's patch, but then
> I checked your current iwlwifi git tree.  There your hw_scan routine
> is commented-out, so I figured you didn't want/need it anymore...?
>
It was never needed in the first place except as an iwlwifi specific hack t=
o=20
minimize any disruption to the current connection. (which often seems to be=
=20
commented out due to firmware issues) mac80211 now does its own PS mode=20
scanning trick along with some frame queuing as a generic means to minimize=
=20
disruptions to the current connection during scans. It still needs some=20
improvements in order to quickly empty the current hardware TX queue before=
=20
commencing a scan and possibly time/segment the scanning such that beacons=
=20
are not lost, but it can certainly be done.

Besides the fact that what hw_scan does can be done by mac80211 for all=20
drivers, the use of the hw_scan callback breaks the AP autoconfiguration co=
de=20
in ieee80211_sta.c due to its inadequate design. Calling hw_scan starts a=20
hardware scan, but there is no way to know when the scan is completed. This=
=20
means the code has no way of knowing when it should look through its scan=20
results and configure itself to connect to an AP if a scan was started by=20
mac80211 for the purpose of finding an AP to connect to.

Even if that problem were addressed, I still wouldn't like it as the design=
 of=20
the hw_scan callback is deficient in a number of other ways and is complete=
ly=20
inapplicable to all other hardware/firmware softmac designs that I know.

=2DMichael Wu

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