Subject: Re: [PATCH v3 net-next 8/8] net: mvneta: add XDP_TX support

From: Lorenzo Bianconi <[email-masked]>
Date: Wed, 16 Oct 2019 12:09:00 +0200

> On Mon, 14 Oct 2019 12:49:55 +0200, Lorenzo Bianconi wrote:
> > Implement XDP_TX verdict and ndo_xdp_xmit net_device_ops function
> > pointer
> > 
> > Signed-off-by: Lorenzo Bianconi <[email-masked]>
> 
> > @@ -1972,6 +1975,109 @@ int mvneta_rx_refill_queue(struct mvneta_port *pp, struct mvneta_rx_queue *rxq)
> >  	return i;
> >  }
> >  
> > +static int
> > +mvneta_xdp_submit_frame(struct mvneta_port *pp, struct mvneta_tx_queue *txq,
> > +			struct xdp_frame *xdpf, bool dma_map)
> > +{
> > +	struct mvneta_tx_desc *tx_desc;
> > +	struct mvneta_tx_buf *buf;
> > +	dma_addr_t dma_addr;
> > +
> > +	if (txq->count >= txq->tx_stop_threshold)
> > +		return MVNETA_XDP_CONSUMED;
> > +
> > +	tx_desc = mvneta_txq_next_desc_get(txq);
> > +
> > +	buf = &txq->buf[txq->txq_put_index];
> > +	if (dma_map) {
> > +		/* ndo_xdp_xmit */
> > +		dma_addr = dma_map_single(pp->dev->dev.parent, xdpf->data,
> > +					  xdpf->len, DMA_TO_DEVICE);
> > +		if (dma_mapping_error(pp->dev->dev.parent, dma_addr)) {
> > +			mvneta_txq_desc_put(txq);
> > +			return MVNETA_XDP_CONSUMED;
> > +		}
> > +		buf->type = MVNETA_TYPE_XDP_NDO;
> > +	} else {
> > +		struct page *page = virt_to_page(xdpf->data);
> > +
> > +		dma_addr = page_pool_get_dma_addr(page) +
> > +			   pp->rx_offset_correction + MVNETA_MH_SIZE;
> > +		dma_sync_single_for_device(pp->dev->dev.parent, dma_addr,
> > +					   xdpf->len, DMA_BIDIRECTIONAL);
> 
> This looks a little suspicious, XDP could have moved the start of frame
> with adjust_head, right? You should also use xdpf->data to find where
> the frame starts, no?

uhm, right..we need to update the dma_addr doing something like:

dma_addr = page_pool_get_dma_addr(page) + xdpf->data - xdpf;

and then use xdpf->len for dma-sync

> 
> > +		buf->type = MVNETA_TYPE_XDP_TX;
> > +	}
> > +	buf->xdpf = xdpf;
> > +
> > +	tx_desc->command = MVNETA_TXD_FLZ_DESC;
> > +	tx_desc->buf_phys_addr = dma_addr;
> > +	tx_desc->data_size = xdpf->len;
> > +
> > +	mvneta_update_stats(pp, 1, xdpf->len, true);
> > +	mvneta_txq_inc_put(txq);
> > +	txq->pending++;
> > +	txq->count++;
> > +
> > +	return MVNETA_XDP_TX;
> > +}
> > +
> > +static int
> > +mvneta_xdp_xmit_back(struct mvneta_port *pp, struct xdp_buff *xdp)
> > +{
> > +	struct xdp_frame *xdpf = convert_to_xdp_frame(xdp);
> > +	int cpu = smp_processor_id();
> > +	struct mvneta_tx_queue *txq;
> > +	struct netdev_queue *nq;
> > +	u32 ret;
> > +
> > +	if (unlikely(!xdpf))
> > +		return MVNETA_XDP_CONSUMED;
> 
> Personally I'd prefer you haven't called a function which return code
> has to be error checked in local variable init.

do you mean moving cpu = smp_processor_id(); after the if condition?

Regards,
Lorenzo

> 
> > +
> > +	txq = &pp->txqs[cpu % txq_number];
> > +	nq = netdev_get_tx_queue(pp->dev, txq->id);
> > +
> > +	__netif_tx_lock(nq, cpu);
> > +	ret = mvneta_xdp_submit_frame(pp, txq, xdpf, false);
> > +	if (ret == MVNETA_XDP_TX)
> > +		mvneta_txq_pend_desc_add(pp, txq, 0);
> > +	__netif_tx_unlock(nq);
> > +
> > +	return ret;
> > +}