On Wednesday 19 January 2011 19:49:03 Jussi Kivilinna wrote: > Quoting Christian Lamparter <chunkeey@xxxxxxxxxxxxxx>: >> On Sunday 09 January 2011 16:46:56 Jussi Kivilinna wrote: >>> Quoting Christian Lamparter <chunkeey@xxxxxxxxxxxxxx>: >>>> this is an interesting one... >>>> >>>> Since zd_beacon_done also uploads the next beacon so long in advance, >>>> there could be an equally long race between the outdated state of the >>>> next beacon's DTIM broadcast traffic indicator (802.11-2007 7.3.2.6) >>>> which -in your case- was uploaded almost a beacon interval ago and >>>> the xmit of ieee80211_get_buffered_bc *now*. >>>> >>>> The dtim bc/mc bit might be not set, when a mc/bc arrived after the >>>> beacon was uploaded, but before the "beacon done event" from the >>>> hardware. So, dozing stations don't expect the broadcast traffic >>>> and of course, they might miss it completely. >>>> >>>> It's probably better to fix this in mac80211 (see the attached hack). >>> >>> Ok, should I add this to my patchset? >> well, difficult to say. As far as I can say, it should be correct for "your >> case". But, on the other hand: what about solutions that can't buffer >> mc/bc frames (and needs to call ieee80211_get_buffered_bc), however the >> firmware is clever enough to maintain a beacon internally (so they >> won't call ieee80211_beacon_get and only relies on set_tim)? >> >> Sure, it's just a unlikely corner case... In fact, I didn't check if >> that's even possible, but it does sound reasonable to some extend. > > From what I checked none of currect driver/device is such. > Maybe if such device appears then !bss->dtim_bc_mc check in > ieee80211_beacon_add_tim() could be masked with driver flag (something > like > IEEE80211_HW_CAN_AND_HANDLE_BEACON_BUT_STILL_NEEDS_HOST_BROADCAST_PS_BUFFERING). True, but a recent discussion into this matter have made parts of the API you are planning to use sort-of "deprecated"? [I think?] http://marc.info/?l=linux-wireless&m=129463297300480 I don't know the exact details, but I'm sure Kvalo does have his reasons. [afaik it has to do with wl12xx, he even explained it once, but I can't find that mail anymore]. >>>> In fact, you could just as well drop "[09/17] zd1211rw: implement >>>> seq_num for IEEE80211_TX_CTL_ASSIGN_SEQ"... unless of course, I'm >>>> an idiot and there is a really clever way around these issues. >>> >>> Oh well, I should have checked this more closely before doing that >>> patch. HW is assigning seq-numbers already and that patch is not needed. >> >> heh, p54's fw can assign sequence numbers as well, but there's a txdesc flag >> to control the counter, so the firmware does not mess with the >> sequence control >> of QoS-Data frames. I hope zd1211* has one too. > > There is tx-control flag that doesn't have effect, but since zd1211 > doesn't appear to support QoS it's not a problem. Ok, that sound reasonable. One more thing, is there a tx-control flag to instruct the HW/FW to write the TSF into probe response frames, just like it does for beacons frames? Sure, this feature is far more important for IBSS, but the 802.11-2007 specs @11.1.4 says that a STA might use beacons or probe responses to synchronize its timers. [However 11.1.1.1 and 11.1.3.4 say that STAs should "only" pick this information from beacons, if I'm not mistaken?!] (Also a uniform "0..0" timestamp in every probe-response looks so sad.) Best Regards, Christian -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
