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Date:   Sun, 6 Sep 2020 10:20:18 +0300
From:   Shay Agroskin <shayagr@...zon.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <davem@...emloft.net>, <lorenzo.bianconi@...hat.com>,
        <brouer@...hat.com>, <echaudro@...hat.com>, <sameehj@...zon.com>,
        <kuba@...nel.org>, <john.fastabend@...il.com>,
        <daniel@...earbox.net>, <ast@...nel.org>
Subject: Re: [PATCH v2 net-next 5/9] net: mvneta: add multi buffer support to XDP_TX


Lorenzo Bianconi <lorenzo@...nel.org> writes:

> Introduce the capability to map non-linear xdp buffer running
> mvneta_xdp_submit_frame() for XDP_TX and XDP_REDIRECT
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 79 
>  +++++++++++++++++----------
>  1 file changed, 49 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/net/ethernet/marvell/mvneta.c 
> b/drivers/net/ethernet/marvell/mvneta.c
> index 4f745a2b702a..65fbed957e4f 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -1854,8 +1854,8 @@ static void mvneta_txq_bufs_free(struct 
> mvneta_port *pp,
>  			bytes_compl += buf->skb->len;
>  			pkts_compl++;
>  			dev_kfree_skb_any(buf->skb);
> -		} else if (buf->type == MVNETA_TYPE_XDP_TX ||
> -			   buf->type == MVNETA_TYPE_XDP_NDO) {
> +		} else if ((buf->type == MVNETA_TYPE_XDP_TX ||
> +			    buf->type == MVNETA_TYPE_XDP_NDO) && 
> buf->xdpf) {
>  			xdp_return_frame(buf->xdpf);
>  		}
>  	}
> @@ -2040,43 +2040,62 @@ 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;
> +	struct skb_shared_info *sinfo = 
> xdp_get_shared_info_from_frame(xdpf);
> +	int i, num_frames = xdpf->mb ? sinfo->nr_frags + 1 : 1;
> +	struct mvneta_tx_desc *tx_desc = NULL;
> +	struct page *page;
>  
> -	if (txq->count >= txq->tx_stop_threshold)
> +	if (txq->count + num_frames >= txq->tx_stop_threshold)
>  		return MVNETA_XDP_DROPPED;
>  
> -	tx_desc = mvneta_txq_next_desc_get(txq);
> +	for (i = 0; i < num_frames; i++) {
> +		struct mvneta_tx_buf *buf = 
> &txq->buf[txq->txq_put_index];
> +		skb_frag_t *frag = i ? &sinfo->frags[i - 1] : 
> NULL;
> +		int len = frag ? skb_frag_size(frag) : xdpf->len;
> +		dma_addr_t dma_addr;
>  
> -	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_DROPPED;
> +		tx_desc = mvneta_txq_next_desc_get(txq);
> +		if (dma_map) {
> +			/* ndo_xdp_xmit */
> +			void *data;
> +
> +			data = frag ? 
> page_address(skb_frag_page(frag))
> +				    : xdpf->data;
> +			dma_addr = 
> dma_map_single(pp->dev->dev.parent, data,
> +						  len, 
> DMA_TO_DEVICE);
> +			if (dma_mapping_error(pp->dev->dev.parent, 
> dma_addr)) {
> +				for (; i >= 0; i--)
> +					mvneta_txq_desc_put(txq);
> +				return MVNETA_XDP_DROPPED;
> +			}
> +			buf->type = MVNETA_TYPE_XDP_NDO;
> +		} else {
> +			page = frag ? skb_frag_page(frag)
> +				    : virt_to_page(xdpf->data);
> +			dma_addr = page_pool_get_dma_addr(page);
> +			if (!frag)
> +				dma_addr += sizeof(*xdpf) + 
> xdpf->headroom;
> + 
> dma_sync_single_for_device(pp->dev->dev.parent,
> +						   dma_addr, len,
> + 
> DMA_BIDIRECTIONAL);
> +			buf->type = MVNETA_TYPE_XDP_TX;
>  		}
> -		buf->type = MVNETA_TYPE_XDP_NDO;
> -	} else {
> -		struct page *page = virt_to_page(xdpf->data);
> +		buf->xdpf = i ? NULL : xdpf;
>  
> -		dma_addr = page_pool_get_dma_addr(page) +
> -			   sizeof(*xdpf) + xdpf->headroom;
> -		dma_sync_single_for_device(pp->dev->dev.parent, 
> dma_addr,
> -					   xdpf->len, 
> DMA_BIDIRECTIONAL);
> -		buf->type = MVNETA_TYPE_XDP_TX;
> +		if (!i)
> +			tx_desc->command = MVNETA_TXD_F_DESC;
> +		tx_desc->buf_phys_addr = dma_addr;
> +		tx_desc->data_size = len;
> +
> +		mvneta_txq_inc_put(txq);
>  	}
> -	buf->xdpf = xdpf;
>  
> -	tx_desc->command = MVNETA_TXD_FLZ_DESC;
> -	tx_desc->buf_phys_addr = dma_addr;
> -	tx_desc->data_size = xdpf->len;
> +	/*last descriptor */
> +	if (tx_desc)
> +		tx_desc->command |= MVNETA_TXD_L_DESC | 
> MVNETA_TXD_Z_PAD;

        When is this condition not taken ? You initialize tx_desc 
        to NULL, but it seems to me like you always set it inside 
        the for loop to the output of mvneta_txq_next_desc_get() 
        which doesn't look like it returns NULL. The for loop runs 1 iteration or `sinfo->nr_frage 
+ 1` iterations (which also equals or larger than 1).

>  
> -	mvneta_txq_inc_put(txq);
> -	txq->pending++;
> -	txq->count++;
> +	txq->pending += num_frames;
> +	txq->count += num_frames;
>  
>  	return MVNETA_XDP_TX;
>  }

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