Re: [PATCH 5.3] mt76: mt76x0e: don't use hw encryption for MT7630E

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Wed, Aug 14, 2019 at 11:50:12AM +0200, Lorenzo Bianconi wrote:
> >
> > Since 41634aa8d6db ("mt76: only schedule txqs from the tx tasklet")
> > I can observe firmware hangs on MT7630E on station mode: tx stop
> > functioning after minor activity (rx keep working) and on module
> > unload device fail to stop with messages:
> >
> > [ 5446.141413] mt76x0e 0000:06:00.0: TX DMA did not stop
> > [ 5449.176764] mt76x0e 0000:06:00.0: TX DMA did not stop
> >
> > Loading module again results in failure to associate with AP.
> > Only machine power off / power on cycle can make device work again.
> >
> > It's unclear why commit 41634aa8d6db causes the problem, but it is
> > related to HW encryption. Since issue is a firmware hang, that is super
> > hard to debug, just disable HW encryption as fix for the issue.
> >
> > Fixes: 41634aa8d6db ("mt76: only schedule txqs from the tx tasklet")
> > Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
> > ---
> >  drivers/net/wireless/mediatek/mt76/mt76x0/pci.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/wireless/mediatek/mt76/mt76x0/pci.c b/drivers/net/wireless/mediatek/mt76/mt76x0/pci.c
> > index 4585e1b756c2..6117e6ca08cb 100644
> > --- a/drivers/net/wireless/mediatek/mt76/mt76x0/pci.c
> > +++ b/drivers/net/wireless/mediatek/mt76/mt76x0/pci.c
> > @@ -62,6 +62,19 @@ static void mt76x0e_stop(struct ieee80211_hw *hw)
> >         mt76x0e_stop_hw(dev);
> >  }
> >
> > +static int
> > +mt76x0e_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
> > +               struct ieee80211_vif *vif, struct ieee80211_sta *sta,
> > +               struct ieee80211_key_conf *key)
> > +{
> > +       struct mt76x02_dev *dev = hw->priv;
> > +
> > +       if (is_mt7630(dev))
> > +               return -EOPNOTSUPP;
> 
> Hi Stanislaw,
> 
> Can you please try if disabling/enabling the tx tasklet during hw key
> configuration fixes the issue?
> Doing something like:
> 
> tasklet_disable(tx_tasklet)
> mt76x02_set_key()
> tasklet_enable(tx_tasklet)

It does not help with the problem.

> Moreover, have you double checked if there is any performance impact
> of not using hw encryption?

I didn't observe any, but realized on this machine I have
aesni_intel encryption accelerator. After rebuild kernel without
CONFIG_CRYPTO_AES_NI_INTEL, 'perf top' showed extra 20% of cpu usage
in aes_encrypt() when sending data with HW encryption disabled.

> If so, I guess it is better to just redefine mt76_wake_tx_queue for
> mt76x0e and run mt76_txq_schedule for 7630e:
> 
> void mt76x0e_wake_tx_queue(struct ieee80211_hw *hw, struct ieee80211_txq *txq)
> {
>         if (is_mt7630(dev)) {
>             mt76_txq_schedule(dev, txq->ac);
>         } else {
>             tasklet_schedule(&dev->tx_tasklet);
>         }
> }

Not sure about reduction of lock contention for which the tx_tasklet
was introduced here, but looks ok for me as fix.
 
Stanislaw