Re: [PATCH v9 4/6] mt76: mt76x02: remove a copy call for usb speedup

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

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> On 12/17/19 10:40 AM, Lorenzo Bianconi wrote:
> >> This patch removes a mt76_wr_copy call from the beacon path to hw.
> >> The skb which is used in this place gets therefore build with txwi
> >> inside its data. For mt76 usb drivers, this saves one synchronuous
> >> copy call over usb, which lets the beacon work complete faster.
> >>
> >> In mmio case, there is not enough headroom to put the txwi into the
> >> skb, it is therefore using an additional mt76_wr_copy, which is fast
> >> over mmio. Thanks Stanislaw for pointing this out.
> >>
> >> Signed-off-by: Markus Theil <markus.theil@tu-ilmenau.de>
> >> ---
> >>  .../wireless/mediatek/mt76/mt76x02_beacon.c   | 20 +++++++++++++++----
> >>  1 file changed, 16 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/net/wireless/mediatek/mt76/mt76x02_beacon.c b/drivers/net/wireless/mediatek/mt76/mt76x02_beacon.c
> >> index 1c4bdf88f712..68a4f512319e 100644
> >> --- a/drivers/net/wireless/mediatek/mt76/mt76x02_beacon.c
> >> +++ b/drivers/net/wireless/mediatek/mt76/mt76x02_beacon.c
> >> @@ -26,15 +26,27 @@ static int
> >>  mt76x02_write_beacon(struct mt76x02_dev *dev, int offset, struct sk_buff *skb)
> >>  {
> >>  	int beacon_len = dev->beacon_ops->slot_size;
> >> -	struct mt76x02_txwi txwi;
> >>  
> >>  	if (WARN_ON_ONCE(beacon_len < skb->len + sizeof(struct mt76x02_txwi)))
> >>  		return -ENOSPC;
> >>  
> >> -	mt76x02_mac_write_txwi(dev, &txwi, skb, NULL, NULL, skb->len);
> >> +	/* USB devices already reserve enough skb headroom for txwi's. This
> >> +	 * helps to save slow copies over USB.
> >> +	 */
> >> +	if (mt76_is_usb(&dev->mt76)) {
> >> +		struct mt76x02_txwi *txwi;
> >> +
> >> +		mt76_insert_hdr_pad(skb);
> > Do we really need mt76_insert_hdr_pad? I think beacon header should be 4B
> > aligned.

mt76_insert_hdr_pad takes into account just 802.11 header length and it is 24
or 28 for mgmt frames.

Regards,
Lorenzo

> >
> > Regards,
> > Lorenzo
> I can leave it out of course, but I don't  know, if beacons from
> mac80211 are always 4B aligned.
> 
> Regards,
> Markus
> >> +		txwi = (struct mt76x02_txwi *)(skb->data - sizeof(*txwi));
> >> +		mt76x02_mac_write_txwi(dev, txwi, skb, NULL, NULL, skb->len);
> >> +		skb_push(skb, sizeof(*txwi));
> >> +	} else {
> >> +		struct mt76x02_txwi txwi;
> >>  
> >> -	mt76_wr_copy(dev, offset, &txwi, sizeof(txwi));
> >> -	offset += sizeof(txwi);
> >> +		mt76x02_mac_write_txwi(dev, &txwi, skb, NULL, NULL, skb->len);
> >> +		mt76_wr_copy(dev, offset, &txwi, sizeof(txwi));
> >> +		offset += sizeof(txwi);
> >> +	}
> >>  
> >>  	mt76_wr_copy(dev, offset, skb->data, skb->len);
> >>  	return 0;
> >> -- 
> >> 2.24.0
> >>
> 

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