TX A-MPDU AGGREGATION(9)

💅 TX A-MPDU aggregation(9) 💅

okay bestie, this is the Kernel API Manual page for TX A-MPDU aggregation, and it’s lowkey essential if you’re doing driver stuff. Aggregation on the TX side requires setting the hardware flag IEEE80211_HW_AMPDU_AGGREGATION. Then the driver will be handed packets with a flag indicating A-MPDU aggregation. The driver or device is responsible for actually aggregating the frames, as well as deciding how many and which to aggregate. No cap, that part is literally on the driver/device. ✨

When TX aggregation is started by some subsystem (usually the rate control algorithm would be appropriate) by calling the ieee80211_start_tx_ba_session function, the driver will be notified via its ampdu_action function, with the IEEE80211_AMPDU_TX_START action. 💖

In response to that, the driver is later required to call the ieee80211_start_tx_ba_cb_irqsafe function, which will really start the aggregation session after the peer has also responded. If the peer responds negatively, the session will be stopped again right away. Note that it is possible for the aggregation session to be stopped before the driver has indicated that it is done setting it up, in which case it must not indicate the setup completion. That’s a major vibe check — don’t skip it. 🫶

Also note that, since we also need to wait for a response from the peer, the driver is notified of the completion of the handshake by the IEEE80211_AMPDU_TX_OPERATIONAL action to the ampdu_action callback. 🦋

Similarly, when the aggregation session is stopped by the peer or something calling ieee80211_stop_tx_ba_session, the driver’s ampdu_action function will be called with the action IEEE80211_AMPDU_TX_STOP. In this case, the call must not fail, and the driver must later call ieee80211_stop_tx_ba_cb_irqsafe. Note that the sta can get destroyed before the BA tear down is complete. 😭 so yeah, handle that carefully.

👀 SEE ALSO 👀

• Kernel file ./net/mac80211/agg-tx.c

okay that’s the whole tea, bestie 🍓 this page lives in ./net/mac80211 and it’s dated October 2026 — mwah 💜