diff options
Diffstat (limited to 'include/net')
| -rw-r--r-- | include/net/mac80211.h | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/include/net/mac80211.h b/include/net/mac80211.h index 3df32a0..bc79930 100644 --- a/include/net/mac80211.h +++ b/include/net/mac80211.h @@ -1539,6 +1539,95 @@ ieee80211_get_alt_retry_rate(const struct ieee80211_hw *hw, */ /** + * DOC: AP support for powersaving clients + * + * In order to implement AP and P2P GO modes, mac80211 has support for + * client powersaving, both "legacy" PS (PS-Poll/null data) and uAPSD. + * There currently is no support for sAPSD. + * + * There is one assumption that mac80211 makes, namely that a client + * will not poll with PS-Poll and trigger with uAPSD at the same time. + * Both are supported, and both can be used by the same client, but + * they can't be used concurrently by the same client. This simplifies + * the driver code. + * + * The first thing to keep in mind is that there is a flag for complete + * driver implementation: %IEEE80211_HW_AP_LINK_PS. If this flag is set, + * mac80211 expects the driver to handle most of the state machine for + * powersaving clients and will ignore the PM bit in incoming frames. + * Drivers then use ieee80211_sta_ps_transition() to inform mac80211 of + * stations' powersave transitions. In this mode, mac80211 also doesn't + * handle PS-Poll/uAPSD. + * + * In the mode without %IEEE80211_HW_AP_LINK_PS, mac80211 will check the + * PM bit in incoming frames for client powersave transitions. When a + * station goes to sleep, we will stop transmitting to it. There is, + * however, a race condition: a station might go to sleep while there is + * data buffered on hardware queues. If the device has support for this + * it will reject frames, and the driver should give the frames back to + * mac80211 with the %IEEE80211_TX_STAT_TX_FILTERED flag set which will + * cause mac80211 to retry the frame when the station wakes up. The + * driver is also notified of powersave transitions by calling its + * @sta_notify callback. + * + * When the station is asleep, it has three choices: it can wake up, + * it can PS-Poll, or it can possibly start a uAPSD service period. + * Waking up is implemented by simply transmitting all buffered (and + * filtered) frames to the station. This is the easiest case. When + * the station sends a PS-Poll or a uAPSD trigger frame, mac80211 + * will inform the driver of this with the @allow_buffered_frames + * callback; this callback is optional. mac80211 will then transmit + * the frames as usual and set the %IEEE80211_TX_CTL_POLL_RESPONSE + * on each frame. The last frame in the service period (or the only + * response to a PS-Poll) also has %IEEE80211_TX_STATUS_EOSP set to + * indicate that it ends the service period; as this frame must have + * TX status report it also sets %IEEE80211_TX_CTL_REQ_TX_STATUS. + * When TX status is reported for this frame, the service period is + * marked has having ended and a new one can be started by the peer. + * + * Another race condition can happen on some devices like iwlwifi + * when there are frames queued for the station and it wakes up + * or polls; the frames that are already queued could end up being + * transmitted first instead, causing reordering and/or wrong + * processing of the EOSP. The cause is that allowing frames to be + * transmitted to a certain station is out-of-band communication to + * the device. To allow this problem to be solved, the driver can + * call ieee80211_sta_block_awake() if frames are buffered when it + * is notified that the station went to sleep. When all these frames + * have been filtered (see above), it must call the function again + * to indicate that the station is no longer blocked. + * + * If the driver buffers frames in the driver for aggregation in any + * way, it must use the ieee80211_sta_set_buffered() call when it is + * notified of the station going to sleep to inform mac80211 of any + * TIDs that have frames buffered. Note that when a station wakes up + * this information is reset (hence the requirement to call it when + * informed of the station going to sleep). Then, when a service + * period starts for any reason, @release_buffered_frames is called + * with the number of frames to be released and which TIDs they are + * to come from. In this case, the driver is responsible for setting + * the EOSP (for uAPSD) and MORE_DATA bits in the released frames, + * to help the @more_data paramter is passed to tell the driver if + * there is more data on other TIDs -- the TIDs to release frames + * from are ignored since mac80211 doesn't know how many frames the + * buffers for those TIDs contain. + * + * If the driver also implement GO mode, where absence periods may + * shorten service periods (or abort PS-Poll responses), it must + * filter those response frames except in the case of frames that + * are buffered in the driver -- those must remain buffered to avoid + * reordering. Because it is possible that no frames are released + * in this case, the driver must call ieee80211_sta_eosp_irqsafe() + * to indicate to mac80211 that the service period ended anyway. + * + * Finally, if frames from multiple TIDs are released from mac80211 + * but the driver might reorder them, it must clear & set the flags + * appropriately (only the last frame may have %IEEE80211_TX_STATUS_EOSP) + * and also take care of the EOSP and MORE_DATA bits in the frame. + * The driver may also use ieee80211_sta_eosp_irqsafe() in this case. + */ + +/** * enum ieee80211_filter_flags - hardware filter flags * * These flags determine what the filter in hardware should be |
