On 2013-06-10 5:11 PM, Simon Wunderlich wrote: > Hey Felix, > > On Fri, Jun 07, 2013 at 07:33:16PM +0200, Felix Fietkau wrote: >> On 2013-06-07 7:05 PM, Simon Wunderlich wrote: >> > This is the follow up from the RFC posted a month ago. This patchset adds generic >> > channel switch support for AP. This is required for DFS operation >> > (e.g. Wi-Fi Alliance requires this for 802.11h certification). This will also >> > be required for IBSS-DFS later. >> > >> > The rough design is: >> > * userspace asks kernel to switch a channel using the new NL80211_CMD_CHANNEL_SWITCH >> > command. It supplies IE information for the time while staying on the old channel and >> > announcing the switch, and IE information for after the switch to the new channel. >> > * IE information contains the beacon and optionally probe responses, which should >> > include (E)CSA IEs for the CSA case. Furthermore an offset is provided (for beacon >> > and probe response) to point to the counter field within the channel switch IEs. >> > * The driver gets the new beacons passed and must set them, and decrement the >> > counter field. When it reaches 0, the channel is changed and userspace notified. >> > >> > Discussion points: >> > * Assembling all these IE information is a little bit tedious but doable (I've >> > patched hostapd). >> > * Other future users like IBSS/MESH will not get the beacon/probe response IEs, as they >> > generate these beacons themselves. Therefore they need the COUNT attribute, which >> > is kind of duplicate right now. >> > * Userspace must generate/handle all IEs, which lifts the previous limitations of >> > the RFC (e.g. no change of band allowed, no operation mode change allowed). >> > * it currently works for me [TM] on my ath9k based machine >> I think this is a bit racy. Just because the driver gets a beacon from >> mac80211 doesn't mean that the beacon will be sent *immediately*. I'd >> recommend calling back from the driver into mac80211 on beacon tx >> completion. Also, it might make sense to skip CAB queue transmissions in >> this case. > > mhm, you're right, changing channel might race with sending the beacon as it's > set right now. I'd change it to: > > * update the counter within get_beacon() (as done now) > * perform the channel switch after beacon transmission is completed (not sure how to get this > event practically yet ... :] ) > > What do you think? > > This must probably handle stuck/lost beacons too - is there any completion function > called for stuck beacons? Right now there are no mac80211 callbacks for either completed or missed beacon tx. Inside ath9k, on AR93xx+, beacons get normal tx completion events. For older chipsets the status descriptor must be checked explicitly - see the implementation of drv_tx_last_beacon. To get the timing right for checking tx completion of the beacon, you can let the normal pre-AR93xx tx completion function check the beacon queue if CSA was indicated via a flag or something. As for stuck beacon, you can hook into the beacon tasklet function. If the driver knows that a CSA is imminent, it can send the notification on a stuck beacon event even before it hits the hw reset (which it only does after several consecutive stuck beacon events). - Felix -- 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
