From 2d7b6e7daf076b63f461ce9c4ec6022ddc3d15bb Mon Sep 17 00:00:00 2001 From: Camelia Groza Date: Mon, 15 Jan 2018 17:42:42 +0200 Subject: [PATCH] sdk_dpaa: update comments about recycling and back-pointer storage Signed-off-by: Camelia Groza --- drivers/net/ethernet/freescale/sdk_dpaa/dpaa_eth_sg.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) --- a/drivers/net/ethernet/freescale/sdk_dpaa/dpaa_eth_sg.c +++ b/drivers/net/ethernet/freescale/sdk_dpaa/dpaa_eth_sg.c @@ -121,6 +121,10 @@ static int _dpa_bp_add_8_bufs(const stru put_page(virt_to_head_page(new_buf)); goto build_skb_failed; } + + /* Store the skb back-pointer before the start of the buffer. + * Otherwise it will be overwritten by the FMan. + */ DPA_WRITE_SKB_PTR(skb, skbh, new_buf, -1); addr = dma_map_single(dev, new_buf, @@ -344,7 +348,10 @@ bool dpa_buf_is_recyclable(struct sk_buf * - buffer address aligned to cacheline bytes * - offset of data from start of buffer no lower than a minimum value * - offset of data from start of buffer no higher than a maximum value + * - the skb back-pointer is stored safely */ + + /* guarantee both the minimum size and the minimum data offset */ new = min(skb_end_pointer(skb) - min_size, skb->data - min_offset); /* left align to the nearest cacheline */ @@ -694,6 +701,9 @@ int __hot skb_to_contig_fd(struct dpa_pr dma_dir = DMA_BIDIRECTIONAL; dma_map_size = dpa_bp->size; + /* Store the skb back-pointer before the start of the buffer. + * Otherwise it will be overwritten by the FMan. + */ DPA_WRITE_SKB_PTR(skb, skbh, buffer_start, -1); *offset = skb_headroom(skb) - fd->offset; } else @@ -711,7 +721,7 @@ int __hot skb_to_contig_fd(struct dpa_pr /* The buffer will be Tx-confirmed, but the TxConf cb must * necessarily look at our Tx private data to retrieve the - * skbuff. (In short: can't use DPA_WRITE_SKB_PTR() here.) + * skbuff. Store the back-pointer inside the buffer. */ DPA_WRITE_SKB_PTR(skb, skbh, buffer_start, 0); } @@ -975,7 +985,11 @@ int __hot skb_to_sg_fd(struct dpa_priv_s fd->length20 = skb->len; fd->offset = priv->tx_headroom; - /* DMA map the SGT page */ + /* DMA map the SGT page + * + * It's safe to store the skb back-pointer inside the buffer since + * S/G frames are non-recyclable. + */ DPA_WRITE_SKB_PTR(skb, skbh, sgt_buf, 0); addr = dma_map_single(dpa_bp->dev, sgt_buf, priv->tx_headroom + sgt_size,