Frame format

As a general rule, when frames are passed between mac80211 and the driver, they start with the IEEE 802.11 header and include the same octets that are sent over the air except for the FCS which should be calculated by the hardware.

There are, however, various exceptions to this rule for advanced features:

The first exception is for hardware encryption and decryption offload where the IV/ICV may or may not be generated in hardware.

Secondly, when the hardware handles fragmentation, the frame handed to the driver from mac80211 is the MSDU, not the MPDU.