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Date:   Wed, 31 Jul 2019 11:09:27 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     linux-wireless@vger.kernel.org, Felix Fietkau <nbd@nbd.name>,
        Ryder Lee <ryder.lee@mediatek.com>, Roy Luo <royluo@google.com>
Subject: Re: [RFC] mt76: fix tx hung regression on MT7630E
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> On Wed, Jul 31, 2019 at 10:19:58AM +0200, Stanislaw Gruszka wrote:
> > On Tue, Jul 30, 2019 at 04:55:31PM +0200, Lorenzo Bianconi wrote:
> > > > > > diff --git a/drivers/net/wireless/mediatek/mt76/mt76x02_mmio.c =
b/drivers/net/wireless/mediatek/mt76/mt76x02_mmio.c
> > > > > > index 467b28379870..622251faa415 100644
> > > > > > --- a/drivers/net/wireless/mediatek/mt76/mt76x02_mmio.c
> > > > > > +++ b/drivers/net/wireless/mediatek/mt76/mt76x02_mmio.c
> > > > > > @@ -170,7 +170,7 @@ static int mt76x02_poll_tx(struct napi_stru=
ct *napi, int budget)
> > > > > >  					       mt76.tx_napi);
> > > > > >  	int i;
> > > > > > =20
> > > > > > -	mt76x02_mac_poll_tx_status(dev, false);
> > > > > > +	mt76x02_mac_poll_tx_status(dev, true);
> > > > >=20
> > > > > I am not sure if we really need mt76x02_mac_poll_tx_status() here=
 since we run
> > > > > it in mt76x02_tx_complete_skb() and in mt76x02_tx_tasklet(). Anyw=
ay the only
> > > > > difference doing so is we do not run mt76x02_send_tx_status().
> > > >=20
> > > > I thought this is the problem, but it was my mistake during testing.
> > > > I tested the above change together with mt76_txq_schedule(dev, txq-=
>ac)
> > > > change and get wrong impression it fixes the issue. But above change
> > > > alone does not help.
> > > >=20
> > > > I tried to add some locking to avoid parallel execution of mt76x02_=
poll_tx()
> > > > and mt76x02_tx_tasklet(), but it didn't help either. So far only pa=
tch
> > > > originally posted here make the problem gone.
> > >=20
> > > so, in order to be on the same page, if you comment out mt76x02_mac_p=
oll_tx_status()
> > > in mt76x02_poll_tx() the issue will still occur. The only to 'fix' it=
 is to run
> > > mt76_txq_schedule_all() in mt76x02_poll_tx(), right?
> >=20
> > Yes.
>=20
> Err, no, I should read more cerfully. It is partiall revert of=20
> 41634aa8d6db ("mt76: only schedule txqs from the tx tasklet") :=20
>=20
> diff --git a/drivers/net/wireless/mediatek/mt76/tx.c b/drivers/net/wirele=
ss/mediatek/mt76/tx.c
> index 5397827668b9..fefe0ee52584 100644
> --- a/drivers/net/wireless/mediatek/mt76/tx.c
> +++ b/drivers/net/wireless/mediatek/mt76/tx.c
> @@ -598,7 +598,7 @@ void mt76_wake_tx_queue(struct ieee80211_hw *hw, stru=
ct ieee80211_txq *txq)
>         if (!test_bit(MT76_STATE_RUNNING, &dev->state))
>                 return;
> =20
> -       tasklet_schedule(&dev->tx_tasklet);
> +       mt76_txq_schedule(dev, txq->ac);
>  }
>  EXPORT_SYMBOL_GPL(mt76_wake_tx_queue);

reviewing the code I think:

- we should not run mt76u_tx_tasklet() from mt76_wake_tx_queue() since we do
  not have tx_napi for usb and it will unnecessary go through tx queue chec=
ks.
  We should probably do in mt76_wake_tx_queue() something like:

  if (is_mmio())
	  tasklet_schedule(&dev->tx_tasklet);
  else
	  mt76_txq_schedule(dev, txq->ac);

  Another solution would be add a status_tasklet that just goes through the=
 tx
  queues receiving the usb tx completion and it schedules the tx_tasklet
  What do you think?

- I guess it does not fix the 76x0e issue but we should just schedule tx qu=
eues in
  mt76x02_tx_tasklet() (like it is done for mt7603 and mt7615) and move sta=
tus
  processing in mt76x02_poll_tx()

Regards,
Lorenzo

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