+ * required to pass up beacons. The hardware is still required to handle
+ * waking up for multicast traffic; if it cannot the driver must handle that
+ * as best as it can, mac80211 is too slow to do that.
+ *
+ * Dynamic powersave is an extension to normal powersave in which the
+ * hardware stays awake for a user-specified period of time after sending a
+ * frame so that reply frames need not be buffered and therefore delayed to
+ * the next wakeup. It's compromise of getting good enough latency when
+ * there's data traffic and still saving significantly power in idle
+ * periods.
+ *
+ * Dynamic powersave is supported by simply mac80211 enabling and disabling
+ * PS based on traffic. Driver needs to only set %IEEE80211_HW_SUPPORTS_PS
+ * flag and mac80211 will handle everything automatically. Additionally,
+ * hardware having support for the dynamic PS feature may set the
+ * %IEEE80211_HW_SUPPORTS_DYNAMIC_PS flag to indicate that it can support
+ * dynamic PS mode itself. The driver needs to look at the
+ * @dynamic_ps_timeout hardware configuration value and use it that value
+ * whenever %IEEE80211_CONF_PS is set. In this case mac80211 will disable
+ * dynamic PS feature in stack and will just keep %IEEE80211_CONF_PS
+ * enabled whenever user has enabled powersave.
+ *
+ * Driver informs U-APSD client support by enabling
+ * %IEEE80211_HW_SUPPORTS_UAPSD flag. The mode is configured through the
+ * uapsd paramater in conf_tx() operation. Hardware needs to send the QoS
+ * Nullfunc frames and stay awake until the service period has ended. To
+ * utilize U-APSD, dynamic powersave is disabled for voip AC and all frames
+ * from that AC are transmitted with powersave enabled.
+ *
+ * Note: U-APSD client mode is not yet supported with
+ * %IEEE80211_HW_PS_NULLFUNC_STACK.
+ */
+
+/**
+ * DOC: Beacon filter support
+ *
+ * Some hardware have beacon filter support to reduce host cpu wakeups
+ * which will reduce system power consumption. It usuallly works so that
+ * the firmware creates a checksum of the beacon but omits all constantly
+ * changing elements (TSF, TIM etc). Whenever the checksum changes the
+ * beacon is forwarded to the host, otherwise it will be just dropped. That
+ * way the host will only receive beacons where some relevant information
+ * (for example ERP protection or WMM settings) have changed.
+ *
+ * Beacon filter support is advertised with the %IEEE80211_HW_BEACON_FILTER
+ * hardware capability. The driver needs to enable beacon filter support
+ * whenever power save is enabled, that is %IEEE80211_CONF_PS is set. When
+ * power save is enabled, the stack will not check for beacon loss and the
+ * driver needs to notify about loss of beacons with ieee80211_beacon_loss().
+ *
+ * The time (or number of beacons missed) until the firmware notifies the
+ * driver of a beacon loss event (which in turn causes the driver to call
+ * ieee80211_beacon_loss()) should be configurable and will be controlled
+ * by mac80211 and the roaming algorithm in the future.
+ *
+ * Since there may be constantly changing information elements that nothing
+ * in the software stack cares about, we will, in the future, have mac80211
+ * tell the driver which information elements are interesting in the sense
+ * that we want to see changes in them. This will include
+ * - a list of information element IDs
+ * - a list of OUIs for the vendor information element
+ *
+ * Ideally, the hardware would filter out any beacons without changes in the
+ * requested elements, but if it cannot support that it may, at the expense
+ * of some efficiency, filter out only a subset. For example, if the device
+ * doesn't support checking for OUIs it should pass up all changes in all
+ * vendor information elements.
+ *
+ * Note that change, for the sake of simplification, also includes information
+ * elements appearing or disappearing from the beacon.
+ *
+ * Some hardware supports an "ignore list" instead, just make sure nothing
+ * that was requested is on the ignore list, and include commonly changing
+ * information element IDs in the ignore list, for example 11 (BSS load) and
+ * the various vendor-assigned IEs with unknown contents (128, 129, 133-136,
+ * 149, 150, 155, 156, 173, 176, 178, 179, 219); for forward compatibility
+ * it could also include some currently unused IDs.
+ *
+ *
+ * In addition to these capabilities, hardware should support notifying the
+ * host of changes in the beacon RSSI. This is relevant to implement roaming
+ * when no traffic is flowing (when traffic is flowing we see the RSSI of
+ * the received data packets). This can consist in notifying the host when
+ * the RSSI changes significantly or when it drops below or rises above
+ * configurable thresholds. In the future these thresholds will also be
+ * configured by mac80211 (which gets them from userspace) to implement
+ * them as the roaming algorithm requires.
+ *
+ * If the hardware cannot implement this, the driver should ask it to
+ * periodically pass beacon frames to the host so that software can do the
+ * signal strength threshold checking.
+ */
+
+/**
+ * DOC: Spatial multiplexing power save
+ *
+ * SMPS (Spatial multiplexing power save) is a mechanism to conserve
+ * power in an 802.11n implementation. For details on the mechanism
+ * and rationale, please refer to 802.11 (as amended by 802.11n-2009)
+ * "11.2.3 SM power save".
+ *
+ * The mac80211 implementation is capable of sending action frames
+ * to update the AP about the station's SMPS mode, and will instruct
+ * the driver to enter the specific mode. It will also announce the
+ * requested SMPS mode during the association handshake. Hardware
+ * support for this feature is required, and can be indicated by
+ * hardware flags.
+ *
+ * The default mode will be "automatic", which nl80211/cfg80211
+ * defines to be dynamic SMPS in (regular) powersave, and SMPS
+ * turned off otherwise.
+ *
+ * To support this feature, the driver must set the appropriate
+ * hardware support flags, and handle the SMPS flag to the config()
+ * operation. It will then with this mechanism be instructed to
+ * enter the requested SMPS mode while associated to an HT AP.