Re: [RFC v2 1/2] mac80211: add a function for setting the TIM bit for a specific station

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2011-02-14 at 15:06 +0100, Felix Fietkau wrote:
> On 2011-02-14 1:09 PM, Johannes Berg wrote:
> > On Wed, 2011-02-09 at 00:32 +0100, Felix Fietkau wrote:
> >> When a driver wants to buffer some frames internally without feeding them
> >> back to mac80211, this allows it to still wake up the station
> > 
> > Why would the driver want to do this though?
> If a station enters powersave and the AP still has buffered frames for
> aggregation, those frames need to stay in the queue, since the driver
> controls the block ack window and keeps some state per frame (e.g.
> number of software retransmissions).
> If ath9k would send those frames back to mac80211, and mac80211 would
> drop some of them, then the client's reorder window would get messed up
> when the client comes back. This would also make managing frame sequence
> numbers more complicated, since the driver would have to skip assigning
> sequence numbers for frames where tx_info->flags has the
> IEEE80211_TX_INTFL_RETRANSMISSION bit set, but then also look for gaps
> caused by expired frames.

Ok, that makes sense. In fact, I think iwlwifi will have the same issue
since it buffers in hw queues... will have to check that.

johannes