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Subject: Re: [PATCH 5.3] mt76: mt76x0e: don't use hw encryption for MT7630E
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        Ryder Lee <ryder.lee@mediatek.com>, Roy Luo <royluo@google.com>
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From:   Felix Fietkau <nbd@nbd.name>
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Date:   Thu, 22 Aug 2019 09:23:52 +0200
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On 2019-08-21 13:22, Stanislaw Gruszka wrote:
> On Wed, Aug 21, 2019 at 12:40:14PM +0200, Felix Fietkau wrote:
>> On 2019-08-21 11:03, Felix Fietkau wrote:
>> > On 2019-08-21 10:47, Stanislaw Gruszka wrote:
>> >> On Tue, Aug 20, 2019 at 01:24:39PM +0200, Stanislaw Gruszka wrote:
>> >>> > Can you test if disabling hw encryption only for shared or only for
>> >>> > pairwise keys makes any difference?
>> >>> 
>> >>> Disabling only pairwise keys helps. Disabling only shared keys does
>> >>> not help.
>> >>> 
>> >>> Not sure if this will be helpful information or make things more
>> >>> confusing, but seems the difference between mt76_txq_schedule()
>> >>> and tasklet_schedule() in mt76_wake_tx_queue() is that on 
>> >>> mt76_txq_schedule() some tx packets are serialized by dev->rx_lock
>> >>> (because some ARP and TCP packets are sent via network stack as response
>> >>> of incoming packet within ieee80211_rx_napi() call). Removing
>> >>> spin_lock(&dev->rx_lock) in mt76_rx_complete() make the problem
>> >>> reproducible again with mt76_txq_schedule() & HW encryption.
>> >> 
>> >> So, I think this is FW/HW issue related with encryption and ordering
>> >> and we should apply patch originally posted in this thread that
>> >> disable HW encryption for MT7630E.
>> >> 
>> >> I do not think we should disable HW encryption only for pairwise keys,
>> >> because FW/HW can have the same bug for shared keys, but is not
>> >> triggered in my test, as we do not sent lot of group frames.
>> > I'm still not convinced that this is just the hardware implementation of
>> > hw crypto being faulty. I think it's more likely that there's a bug in
>> > the tx path somewhere, which causes hangs on MT7630E but remains hidden
>> > (or at least recoverable) on other devices.
>> > I'm currently reviewing key handling in the mac80211 fast-xmit codepath
>> > and get the feeling that something might be racy there.
>> > I will let you know when I make some progress with that review.
>> > If we can't find the bug soon, then I'm fine with merging this patch.
>> > Right now, I would like to see first if we can fix it properly.
>> Another question: Does a watchdog restart happen before tx fails?
> 
> No, we do not run wdt_work for mt76x0e.
I didn't find anything conclusive yet, so I agree with merging this
patch for now until we have a better fix.

- Felix