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

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> 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.

Regards,
Lorenzo

> +		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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