linux-kernel - Re: [PATCH wireless 2/5] wifi: b43: Stop/wake correct queue in DMA Tx path when QoS is disabled

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Date: Sat, 30 Dec 2023 17:15:18 +0000
From: Rahul Rameshbabu <sergeantsagara@...tonmail.com>
To: Michael Büsch <m@...s.ch>
Cc: Julian Calaby <julian.calaby@...il.com>, Kalle Valo <kvalo@...nel.org>, linux-wireless@...r.kernel.org, b43-dev@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH wireless 2/5] wifi: b43: Stop/wake correct queue in DMA Tx path when QoS is disabled

On Sat, 30 Dec, 2023 14:40:36 +0100 Michael Büsch <m@...s.ch> wrote:
> [[PGP Signed Part:Undecided]]
> On Sat, 30 Dec 2023 18:48:45 +1100
> Julian Calaby <julian.calaby@...il.com> wrote:
>> > --- a/drivers/net/wireless/broadcom/b43/dma.c
>> > +++ b/drivers/net/wireless/broadcom/b43/dma.c
>> > @@ -1399,7 +1399,10 @@ int b43_dma_tx(struct b43_wldev *dev, struct sk_buff *skb)
>> >             should_inject_overflow(ring)) {
>> >                 /* This TX ring is full. */
>> >                 unsigned int skb_mapping = skb_get_queue_mapping(skb);
>> > -               ieee80211_stop_queue(dev->wl->hw, skb_mapping);
>> > +               if (dev->qos_enabled)
>> > +                       ieee80211_stop_queue(dev->wl->hw, skb_mapping);
>> > +               else
>> > +                       ieee80211_stop_queue(dev->wl->hw, 0);  
>> 
>> Would this be a little cleaner if we only look up the queue mapping if
>> QOS is enabled? I.e.
>
> No. It would break the other uses of skb_mapping.
>
> But I am wondering why skb_mapping is non-zero in the first place.
> I think the actual bug might be somewhere else.

Right, skb_mapping is used to map to the correct software structures DMA
mapped to the device. The reason the mapping for the best effort queue
(the default/defacto when QoS is disabled) is not zero is due to the way
initialization of the queues/rings occurs in the driver. The best effort
queue is mapped as the third queue, which leads to this issue when QoS
is disabled. Would it make more sense to change the mappings in
initialization such that the best effort queue is by default mapped to
zero, so we would not need such conditionals?

--
Thanks,

Rahul Rameshbabu