linux-kernel - Re: [PATCH 2/3] mac80211: Add support to trigger sta disconnect on hardware restart

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Date:   Fri, 5 Feb 2021 13:51:49 -0800
From:   Abhishek Kumar <kuabhs@...omium.org>
To:     Youghandhar Chintala <youghand@...eaurora.org>
Cc:     Felix Fietkau <nbd@....name>,
        Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        Rakesh Pillai <pillair@...eaurora.org>
Subject: Re: [PATCH 2/3] mac80211: Add support to trigger sta disconnect on
 hardware restart

Since using DELBA frame to APs to re-establish BA session has a
dependency on APs and also some APs may not honour the DELBA frame. I
am fine with having the disconnect/reconnect solution. The change
looks good to me.

Reviewed-by: Abhishek Kumar <kuabhs@...omium.org>

Thanks
Abhishek

On Thu, Jan 28, 2021 at 12:08 AM <youghand@...eaurora.org> wrote:
>
> On 2020-12-15 23:10, Felix Fietkau wrote:
> > On 2020-12-15 18:23, Youghandhar Chintala wrote:
> >> Currently in case of target hardware restart, we just reconfig and
> >> re-enable the security keys and enable the network queues to start
> >> data traffic back from where it was interrupted.
> >>
> >> Many ath10k wifi chipsets have sequence numbers for the data
> >> packets assigned by firmware and the mac sequence number will
> >> restart from zero after target hardware restart leading to mismatch
> >> in the sequence number expected by the remote peer vs the sequence
> >> number of the frame sent by the target firmware.
> >>
> >> This mismatch in sequence number will cause out-of-order packets
> >> on the remote peer and all the frames sent by the device are dropped
> >> until we reach the sequence number which was sent before we restarted
> >> the target hardware
> >>
> >> In order to fix this, we trigger a sta disconnect, for the targets
> >> which expose this corresponding wiphy flag, in case of target hw
> >> restart. After this there will be a fresh connection and thereby
> >> avoiding the dropping of frames by remote peer.
> >>
> >> The right fix would be to pull the entire data path into the host
> >> which is not feasible or would need lots of complex changes and
> >> will still be inefficient.
> > How about simply tracking which tids have aggregation enabled and send
> > DELBA frames for those after the restart?
> > It would mean less disruption for affected stations and less ugly hacks
> > in the stack for unreliable hardware.
> >
> > - Felix
>
> Hi Felix,
>
> We did try to send an ADDBA frame to the AP once the SSR happened. The
> AP ack’ed the frame and the new BA session with renewed sequence number
> was established. But still, the AP did not respond to the ping requests
> with the new sequence number. It did not respond until one of the two
> happened.
> 1.      The sequence number was more than the sequence number that DUT had
> used before SSR happened
> 2.      DUT disconnected and then reconnected.
> The other option is to send a DELBA frame to the AP and make the AP also
> force to establish the BA session from its side. This we feel can have
> some interoperability issues as some of the AP’s may not honour the
> DELBA frame and will continue to use the earlier BA session that it had
> established. Given that re-negotiating the BA session is prone to IOT
> issues, we feel that it would be good to go with the
> Disconnect/Reconnect solution which is foolproof and will work in all
> scenarios.
>
> Regards,
> Youghandhar