Re: [PATCH net-next] eth: bnxt: add netmem TX support

Taehee Yoo
2025-06-18T13:43:06Z

On Wed, Jun 18, 2025 at 5:27 AM Stanislav Fomichev <stfomichev@gmail.com> wrote:
>

Hi Stanislav,
Thanks a lot for your review!

> On 06/17, Taehee Yoo wrote:
> > Use netmem_dma_*() helpers and declare netmem_tx to support netmem TX.
> > By this change, all bnxt devices will support the netmem TX.
> >
> > bnxt_start_xmit() uses memcpy() if a packet is too small. However,
> > netmem packets are unreadable, so memcpy() is not allowed.
> > It should check whether an skb is readable, and if an SKB is unreadable,
> > it is processed by the normal transmission logic.
> >
> > netmem TX can be tested with ncdevmem.c
> >
> > Signed-off-by: Taehee Yoo <ap420073@gmail.com>
> > ---
> > drivers/net/ethernet/broadcom/bnxt/bnxt.c | 28 ++++++++++++++---------
> > 1 file changed, 17 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > index 869580b6f70d..4de9dc123a18 100644
> > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > @@ -477,6 +477,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > struct bnxt_tx_ring_info *txr;
> > struct bnxt_sw_tx_bd *tx_buf;
> > __le32 lflags = 0;
> > + skb_frag_t *frag;
> >
> > i = skb_get_queue_mapping(skb);
> > if (unlikely(i >= bp->tx_nr_rings)) {
> > @@ -563,7 +564,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > lflags |= cpu_to_le32(TX_BD_FLAGS_NO_CRC);
> >
> > if (free_size == bp->tx_ring_size && length <= bp->tx_push_thresh &&
> > - !lflags) {
> > + skb_frags_readable(skb) && !lflags) {
> > struct tx_push_buffer *tx_push_buf = txr->tx_push;
> > struct tx_push_bd *tx_push = &tx_push_buf->push_bd;
> > struct tx_bd_ext *tx_push1 = &tx_push->txbd2;
> > @@ -598,9 +599,9 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > skb_copy_from_linear_data(skb, pdata, len);
> > pdata += len;
> > for (j = 0; j < last_frag; j++) {
> > - skb_frag_t *frag = &skb_shinfo(skb)->frags[j];
> > void *fptr;
> >
> > + frag = &skb_shinfo(skb)->frags[j];
> > fptr = skb_frag_address_safe(frag);
> > if (!fptr)
> > goto normal_tx;
> > @@ -708,8 +709,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > cpu_to_le32(cfa_action << TX_BD_CFA_ACTION_SHIFT);
> > txbd0 = txbd;
> > for (i = 0; i < last_frag; i++) {
> > - skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
> > -
> > + frag = &skb_shinfo(skb)->frags[i];
> > prod = NEXT_TX(prod);
> > txbd = &txr->tx_desc_ring[TX_RING(bp, prod)][TX_IDX(prod)];
> >
> > @@ -721,7 +721,8 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > goto tx_dma_error;
> >
> > tx_buf = &txr->tx_buf_ring[RING_TX(bp, prod)];
> > - dma_unmap_addr_set(tx_buf, mapping, mapping);
> > + netmem_dma_unmap_addr_set(skb_frag_netmem(frag), tx_buf,
> > + mapping, mapping);
> >
> > txbd->tx_bd_haddr = cpu_to_le64(mapping);
> >
> > @@ -778,9 +779,11 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > for (i = 0; i < last_frag; i++) {
> > prod = NEXT_TX(prod);
> > tx_buf = &txr->tx_buf_ring[RING_TX(bp, prod)];
> > - dma_unmap_page(&pdev->dev, dma_unmap_addr(tx_buf, mapping),
> > - skb_frag_size(&skb_shinfo(skb)->frags[i]),
> > - DMA_TO_DEVICE);
> > + frag = &skb_shinfo(skb)->frags[i];
> > + netmem_dma_unmap_page_attrs(&pdev->dev,
> > + dma_unmap_addr(tx_buf, mapping),
> > + skb_frag_size(frag),
> > + DMA_TO_DEVICE, 0);
> > }
> >
> > tx_free:
> > @@ -3422,9 +3425,11 @@ static void bnxt_free_one_tx_ring_skbs(struct bnxt *bp,
> > skb_frag_t *frag = &skb_shinfo(skb)->frags[j];
> >
> > tx_buf = &txr->tx_buf_ring[ring_idx];
> > - dma_unmap_page(&pdev->dev,
> > - dma_unmap_addr(tx_buf, mapping),
> > - skb_frag_size(frag), DMA_TO_DEVICE);
> > + netmem_dma_unmap_page_attrs(&pdev->dev,
> > + dma_unmap_addr(tx_buf,
> > + mapping),
> > + skb_frag_size(frag),
> > + DMA_TO_DEVICE, 0);
> > }
> > dev_kfree_skb(skb);
> > }
> > @@ -16713,6 +16718,7 @@ static int bnxt_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
> > if (BNXT_SUPPORTS_QUEUE_API(bp))
> > dev->queue_mgmt_ops = &bnxt_queue_mgmt_ops;
> > dev->request_ops_lock = true;
> > + dev->netmem_tx = true;
> >
> > rc = register_netdev(dev);
> > if (rc)
>
> Acked-by: Stanislav Fomichev <sdf@fomichev.me>
>
> Similar to what I had internally for testing. One thing to think about
> here might be to put that netmem_tx=true under BNXT_SUPPORTS_QUEUE_API
> conditional. This way both rx/tx will either be supported or not. But
> since there is probably no real FW requirement for TX, should be good
> as is.

I agree with you.
Since netmem TX doesn't require any specific hardware or firmware
features, it should be safe to enable this for all bnxt devices.

Thanks a lot!
Taehee Yoo