Re: [PATCH] wifi: mt76: mt7603: discard power-save loopbacks after wakeup

[Cristian Papa <pcristian292@gmail.com>]

On 20.10.26 11:48, Felix Fietkau wrote:
> On 14.10.26 08:22, Cristian Papa wrote:
>> Discard late frames rather than retransmitting their old sequence and
>> packet numbers after newer traffic or a wakeup BAR. This loses the late
>> frame; it does not recover delivery. Use the station's sleep state, not
>> the temporary hardware PS bypass used during U-APSD service periods.
> Why did you decide to drop them instead of pushing them to immediate tx?

Hi Felix, thanks for looking at it.

Because the looped-back frame keeps the TXD it was first queued with.
mt7603_mac_write_txwi() puts the 802.11 sequence number in the TXD with
SN_VALID, and with a hardware key it also takes the PN from key->tx_pn at
that point. mt7603_rx_loopback_skb() only rewrites Q_IDX, so a late frame
pushed to immediate TX would go out with its original SN and PN.

On wakeup, mt7603_sta_ps() sends the psq ahead of the newer traffic, so
the order holds there. A loopback that arrives after that drain is older
than frames that may already have gone out with newer SN/PN. With CCMP the
peer's replay check would drop it, in an aggregation session it can fall
behind the window after the newer frames or the BAR, and on an open link
it would arrive out of order. So I expected immediate TX to mostly spend
airtime on a frame the peer discards.

I haven't measured how late these loopbacks arrive, though. One that
arrives before the newer frames go out would still be delivered in order.
If you'd rather push them to immediate TX, I can send a v2 that does that.

Cristian