iwlwifi workaround for mac80211 sequence number bug

[Johannes Berg <johannes@sipsolutions.net>]

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Ok, so I'm frustrated. I spent a few hours today chasing docs, trying to
understand sequence numbering from the specs, how we implement it in
mac80211 for TX and RX, how hardware/firmware implements it. Finally, I
figure out that mac80211 is buggy, and come up with a buggy (now I know)
patch.

Then, now, I find out that iwlwifi contains a workaround for the
mac80211 sequence numbering, so you've known all along!

Why don't you tell anyone about the problems you find? It can't be that
hard. Are there any other lurking issues like that?

Here's the code from iwlwifi:

        if (ieee80211_is_data_qos(fc)) {
                qc = ieee80211_get_qos_ctl(hdr);
                tid = qc[0] & 0xf;
                seq_number = priv->stations[sta_id].tid[tid].seq_number &
                                IEEE80211_SCTL_SEQ;
                hdr->seq_ctrl = cpu_to_le16(seq_number) |
                        (hdr->seq_ctrl &
                                __constant_cpu_to_le16(IEEE80211_SCTL_FRAG));
                seq_number += 0x10;
                /* aggregation is on for this <sta,tid> */
                if (info->flags & IEEE80211_TX_CTL_AMPDU)
                        txq_id = priv->stations[sta_id].tid[tid].agg.txq_id;
                priv->stations[sta_id].tid[tid].tfds_in_queue++;
        }

We can implement that trivially in mac80211 and make it do the right
thing for all drivers instead of having iwlwifi work around the bug in
mac80211.

Additionally, we can then remove the ssn argument to the ampdu_action
callback.

johannes

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