On Mon, Feb 23, 2009 at 11:31 AM, Kalle Valo <kalle.valo@xxxxxx> wrote: > "Luis R. Rodriguez" <mcgrof@xxxxxxxxx> writes: > >> On Mon, Feb 23, 2009 at 11:06 AM, Kalle Valo <kalle.valo@xxxxxx> wrote: >>> >>>> For the case or cards capable of 5 GHz or of HT I believe we should >>>> consider the cases of dealing with DFS or HT channel switch both of >>>> which can occur dynamically while the STAs are associated. If >>>> hardware is capable of differentiating this (through beacon >>>> checksums) then that's an enhancement but for now I suspect that is >>>> not the case for most hardware that implements this and as such for >>>> the case when on DFS or using HT we can simply have mac80211 disable >>>> this. Not sure... Thoughts? >>> >>> I don't see a problem. Like you said, such hardware should have beacon >>> checksumming support. Whenever the checksum has changed, the hardware >>> should pass the beacon to the host and mac80211 would receive the >>> beacon just like without beacon filtering. >> >> _should_ -- but I don't think this is yet implemented. > > This is transparent for mac80211, if that's what you are asking. Even > though the beacon filtering feature is enabled, the hardware can still > send as much as beacons it wants. The most important is that the > driver will call ieee80211_beacon_loss() whenever beacons are lost > because mac80211 will not be following them. > >>> Beacon filtering can be thought like filtering unrelevant beacons, but >>> passing through the beacons which have new information. For example, >>> stlc45xx already has beacon checksum support even though it doesn't >>> support 5 GHz band. Unfortunately I haven't managed to find the time >>> to test it yet. >> >> As IEEE-802.11 advances how does the hardware know which IEs to >> checksum or not for? :) > > This is what is documented about stlc45xx firmware beacon filtering: > > "The LM_PSM_CHECKSUM flag configures the LMAC to calculate a checksum > over the beacon frame body. The checksum is calculated over the > frame-body, starting after the timestamp element. Excluded from the > checksum calculation are all flexible elements, with a corresponding > element ID in the exclude array structure member. The beacon is > forwarded to the application, if the checksum changes from the > previous received beacon." > > So the host can just provide the element ids which need to be excluded. How does the hardware deal with IEs that may change order? I am not sure how common this is but I do wonder. Luis -- 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
