Re: [PATCH] iwlagn: default to MAX_UCODE_BEACON_INTERVAL in iwl_adjust_beacon_interval

["John W. Linville" <linville@tuxdriver.com>]

On Sat, Feb 21, 2009 at 09:31:33AM -0800, reinette chatre wrote:
> On Fri, 2009-02-20 at 16:31 -0800, John W. Linville wrote:
> > From: John W. Linville <linville@tuxdriver.com>
> > 
> > Default to MAX_UCODE_BEACON_INTERVAL if the output of
> > iwl_adjust_beacon_interval would otherwise be zero.  This prevents a
> > division by zero on my iwl5300-equipped Lenovo T400 with kernels that
> > include "mac80211: use cfg80211s BSS infrastructure".
> > 
> > This patch is a bit of a hack -- I'm not sure why iwl_setup_rxon_timing
> > is giving iwl_adjust_beacon_interval a zero input (which is the only way
> > it would output zero).  I would be happy to have a better fix.  But for
> > now, this makes my box boot...
> > 
> > Signed-off-by: John W. Linville <linville@tuxdriver.com>
> 
> Unfortunately I do not have a better fix, but I could shed some light
> onto what may be going on and hope we can together figure out what is
> the problem.
> 
> First, it appears that your problem occurs during association. The
> driver obtains the value of beacon interval from mac80211 at the time it
> is asked to associate (specifically, mac80211 calls bss_info_changed
> with BSS_CHANGED_ASSOC and ieee80211_bss_conf->assoc is true). The
> driver obtains beacon interval from iee80211_bss_conf structure at this
> time. As you indicate - the driver gets a zero and this causes an oops
> later.
> 
> Now, the patch you pointed out ("mac80211: use cfg80211s BSS
> infrastructure") changes the way in which the beacon interval value is
> obtained and stored ... but yet I cannot see how it can be different
> from before and cause zero to be returned. Here I hope that Johannes can
> shed some light.
> 
> Before this patch we used mac80211's BSS infrastructure and placed the
> beacon interval from the beacon frame in that. Now we use cfg80211's BSS
> infrastructure and place the beacon interval from the probe response in
> that. Now, the function that does this (ieee80211_bss_info_update) does
> not currently distinguish between beacon and probe resp when it updates
> the BSS information and uses the probe resp fields (in
> cfg80211_inform_bss_frame). This should not matter because the beacon
> and probe resp fields are the same in this regard.
> 
> So ... if the information is obtained in the same way there could maybe
> be an issue in how it is stored now? This has also changed significantly
> with the move to the rbtree. I don't know.

I'm sorry if I was too terse, but at least it had the benefit
of you reproducing my struggle and my analysis (and my perplexed
frustration). :-)

> Johannes, do you perhaps know how beacon interval was ok with the
> mac80211 BSS infrastructure, but now we get zero after moving to
> cfg80211 BSS infrastructure?

Help us Obi Wan Johannes...you're our only hope! :-)

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville@tuxdriver.com			might be all we have.  Be ready.