On Thursday 20 January 2011 09:16:06 Jussi Kivilinna wrote: > Quoting Christian Lamparter <chunkeey@xxxxxxxxxxxxxx>: >> 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>: >>>>>> 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 there could be an equally long race between the outdated state of the 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]. >> > > What I understood from that thread is that rt2x00/usb doesn't have HW > buffering and doesn't enable IEEE80211_HW_HOST_BROADCAST_PS_BUFFERING > (rt2x00/pci does), and yet enables AP-mode. Driver has this comment: > /* > * Initialize all hw fields. > * > * Don't set IEEE80211_HW_HOST_BROADCAST_PS_BUFFERING unless we are > * capable of sending the buffered frames out after the DTIM > * transmission using rt2x00lib_beacondone. This will send out > * multicast and broadcast traffic immediately instead of buffering it > * infinitly and thus dropping it after some time. > */ My bad, you are right. This is not something to worry about anymore. > > 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.) > > > > No such flag I'm afraid. Vendor driver appears to be reading > tsf-register from driver and writing value to probe response frames, > maybe something I should add to zd1211rw too. It's more of a cosmetic thing, but very difficult to get it right without firmware/hw support [over an usb]. So you might just leave it as it is... 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
