Re: [PATCH net-next v2 4/5] net: lan966x: Add support for XDP_TX

Alexander Lobakin
2022-11-16T15:35:03Z

From: Horatiu Vultur <horatiu.vultur@microchip.com>
Date: Tue, 15 Nov 2022 22:44:55 +0100

Extend lan966x XDP support with the action XDP_TX. In this case when the
received buffer needs to execute XDP_TX, the buffer will be moved to the
TX buffers. So a new RX buffer will be allocated.
When the TX finish with the frame, it would release completely this
buffer.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
---
.../ethernet/microchip/lan966x/lan966x_fdma.c | 78 +++++++++++++++++--
.../ethernet/microchip/lan966x/lan966x_main.c | 4 +-
.../ethernet/microchip/lan966x/lan966x_main.h | 8 ++
.../ethernet/microchip/lan966x/lan966x_xdp.c | 8 ++
4 files changed, 91 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
index 384ed34197d58..c2e56233a8da5 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
@@ -394,13 +394,21 @@ static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
dcb_buf->dev->stats.tx_bytes += dcb_buf->len;

dcb_buf->used = false;
- dma_unmap_single(lan966x->dev,
- dcb_buf->dma_addr,
- dcb_buf->len,
- DMA_TO_DEVICE);
- if (!dcb_buf->ptp)
+ if (dcb_buf->skb)
+ dma_unmap_single(lan966x->dev,
+ dcb_buf->dma_addr,
+ dcb_buf->len,
+ DMA_TO_DEVICE);
+
+ if (dcb_buf->skb && !dcb_buf->ptp)
dev_kfree_skb_any(dcb_buf->skb);

+ if (dcb_buf->page) {
+ page_pool_release_page(lan966x->rx.page_pool,
+ dcb_buf->page);
+ put_page(dcb_buf->page);
+ }

Hmm, that's not really correct.

For skb, you need to unmap + free, true (BPW, just use
napi_consume_skb()).
For %XDP_TX, as you use Page Pool, you don't need to unmap, but you
need to do xdp_return_frame{,_bulk}. Plus, as Tx is being done here
directly from an Rx NAPI polling cycle, xdp_return_frame_rx_napi()
is usually used. Anyway, each of xdp_return_frame()'s variants will
call page_pool_put_full_page() for you.
For %XDP_REDIRECT, as you don't know the source of the XDP frame,
you need to unmap it (as it was previously mapped in
::ndo_xdp_xmit()), plus call xdp_return_frame{,_bulk} to free the
XDP frame. Note that _rx_napi() variant is not applicable here.

That description might be confusing, so you can take a look at the
already existing code[0] to get the idea. I think this piece shows
the expected logics rather well.

+
clear = true;
}

@@ -532,6 +540,9 @@ static int lan966x_fdma_napi_poll(struct napi_struct *napi, int weight)
lan966x_fdma_rx_free_page(rx);
lan966x_fdma_rx_advance_dcb(rx);
goto allocate_new;
+ case FDMA_TX:
+ lan966x_fdma_rx_advance_dcb(rx);
+ continue;
case FDMA_DROP:
lan966x_fdma_rx_free_page(rx);
lan966x_fdma_rx_advance_dcb(rx);
@@ -653,6 +664,62 @@ static void lan966x_fdma_tx_start(struct lan966x_tx *tx, int next_to_use)
tx->last_in_use = next_to_use;
}

+int lan966x_fdma_xmit_xdpf(struct lan966x_port *port,
+ struct xdp_frame *xdpf,
+ struct page *page)
+{
+ struct lan966x *lan966x = port->lan966x;
+ struct lan966x_tx_dcb_buf *next_dcb_buf;
+ struct lan966x_tx *tx = &lan966x->tx;
+ dma_addr_t dma_addr;
+ int next_to_use;
+ __be32 *ifh;
+ int ret = 0;
+
+ spin_lock(&lan966x->tx_lock);
+
+ /* Get next index */
+ next_to_use = lan966x_fdma_get_next_dcb(tx);
+ if (next_to_use < 0) {
+ netif_stop_queue(port->dev);
+ ret = NETDEV_TX_BUSY;
+ goto out;
+ }
+
+ /* Generate new IFH */
+ ifh = page_address(page) + XDP_PACKET_HEADROOM;
+ memset(ifh, 0x0, sizeof(__be32) * IFH_LEN);
+ lan966x_ifh_set_bypass(ifh, 1);
+ lan966x_ifh_set_port(ifh, BIT_ULL(port->chip_port));
+
+ dma_addr = page_pool_get_dma_addr(page);
+ dma_sync_single_for_device(lan966x->dev, dma_addr + XDP_PACKET_HEADROOM,
+ xdpf->len + IFH_LEN_BYTES,
+ DMA_TO_DEVICE);

Also not correct. This page was mapped with %DMA_FROM_DEVICE in the
Rx code, now you sync it for the opposite.
Most drivers in case of XDP enabled create Page Pools with ::dma_dir
set to %DMA_BIDIRECTIONAL. Now you would need only to sync it here
with the same direction (bidir) and that's it.

+
+ /* Setup next dcb */
+ lan966x_fdma_tx_setup_dcb(tx, next_to_use, xdpf->len + IFH_LEN_BYTES,
+ dma_addr + XDP_PACKET_HEADROOM);
+
+ /* Fill up the buffer */
+ next_dcb_buf = &tx->dcbs_buf[next_to_use];
+ next_dcb_buf->skb = NULL;
+ next_dcb_buf->page = page;
+ next_dcb_buf->len = xdpf->len + IFH_LEN_BYTES;
+ next_dcb_buf->dma_addr = dma_addr;
+ next_dcb_buf->used = true;
+ next_dcb_buf->ptp = false;
+ next_dcb_buf->dev = port->dev;
+
+ /* Start the transmission */
+ lan966x_fdma_tx_start(tx, next_to_use);
+
+out:
+ spin_unlock(&lan966x->tx_lock);
+
+ return ret;
+}
+
int lan966x_fdma_xmit(struct sk_buff *skb, __be32 *ifh, struct net_device *dev)
{
struct lan966x_port *port = netdev_priv(dev);
@@ -709,6 +776,7 @@ int lan966x_fdma_xmit(struct sk_buff *skb, __be32 *ifh, struct net_device *dev)
/* Fill up the buffer */
next_dcb_buf = &tx->dcbs_buf[next_to_use];
next_dcb_buf->skb = skb;
+ next_dcb_buf->page = NULL;
next_dcb_buf->len = skb->len;
next_dcb_buf->dma_addr = dma_addr;
next_dcb_buf->used = true;

[...]

--
2.38.0

Thanks,
Olek