Re: [PATCH v3 1/1] mac80211: tell driver when dtim change detected

["Luis R. Rodriguez" <mcgrof@gmail.com>]

On Fri, Jan 22, 2010 at 4:11 PM, Guy, Wey-Yi <wey-yi.w.guy@intel.com> wrote:
> On Fri, 2010-01-22 at 15:44 -0800, Luis R. Rodriguez wrote:
>> On Fri, Jan 22, 2010 at 11:46 AM, Johannes Berg
>> <johannes@sipsolutions.net> wrote:
>> > On Fri, 2010-01-22 at 11:20 -0800, Luis R. Rodriguez wrote:
>> >
>> >> > Previously, we would switch the channel completely to the new operating
>> >> > channel before even probing the AP. That way, we would virtually always
>> >> > receive a beacon from the new AP between the time we started the
>> >> > association process (probe,auth,assoc) and configuring the driver.
>> >> >
>> >> > Now with the new changes that use the off-channel work, we may return to
>> >> > the old "operating" channel, which may be no particular channel, between
>> >> > all these steps. Thus, if there's no beacon between any of probe
>> >> > request/response, auth "request"/"response", assoc request/response, we
>> >> > never get one, and this situation happens.
>> >> >
>> >> > I see two solutions, apart from this special-case patch fixing
>> >> >
>> >> > First, we could go back to the original behaviour if we have just one
>> >> > virtual interface. But that still leaves us with the race, we might do
>> >> > all three frame exchanges within a beacon interval and still miss the
>> >> > beacon, we just tend to not do that and get a beacon.
>> >>
>> >> Curious, what symptoms were seen when the dtim was not propagated
>> >> prior to association, did the STA just not wake up for the right dtim
>> >> interval when in PS mode?
>> >
>> > Yes, I don't really know exactly what happens,
>>
>> OK -- Wey, can you elaborate a little as to how you found this and
>> what you were seeing? Does the device not go into PS mode at all?
>
> We are doing Power consumption test with different DTIM value, the test
> is based on test scripts, so we disable the NetworkManager to make sure
> we can control which AP we need to associated with. During the test, we
> notice when AP change it DTIM value, a lot time STA will used the old
> DTIM value in Power Save mode which cause problem.

Ah I see. What if there was no old dtim value before?

> We believe the correct fix is mac80211 should wait for both probe
> response and beacon arrived before start the association process.
>
> Hope this explain what we found.

Indeed, thanks a lot.

  Luis