netdev - [PATCH net-next v2 2/8] i40e: change Rx buffer size for legacy-rx to support XDP multi-buffer

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Message-Id: <20230309212819.1198218-3-anthony.l.nguyen@intel.com>
Date:   Thu,  9 Mar 2023 13:28:13 -0800
From:   Tony Nguyen <anthony.l.nguyen@...el.com>
To:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, netdev@...r.kernel.org
Cc:     Tirthendu Sarkar <tirthendu.sarkar@...el.com>,
        anthony.l.nguyen@...el.com, maciej.fijalkowski@...el.com,
        magnus.karlsson@...el.com, ast@...nel.org, daniel@...earbox.net,
        hawk@...nel.org, john.fastabend@...il.com, bpf@...r.kernel.org,
        Chandan Kumar Rout <chandanx.rout@...el.com>
Subject: [PATCH net-next v2 2/8] i40e: change Rx buffer size for legacy-rx to support XDP multi-buffer

From: Tirthendu Sarkar <tirthendu.sarkar@...el.com>

Adding support for XDP multi-buffer entails adding information of all
the fragments of the packet in the xdp_buff. This approach implies that
underlying buffer has to provide tailroom for skb_shared_info.

In the legacy-rx mode, driver can only configure up to 2k sized Rx buffers
and with the current configuration of 2k sized Rx buffers there is no way
to do tailroom reservation for skb_shared_info. Hence size of Rx buffers
is now lowered to 2048 - sizeof(skb_shared_info). Also, driver can only
chain up to 5 Rx buffers and this means max MTU supported for legacy-rx
is now 8614 (5 * rx_buffer_len  - ETH header with VLAN).

Signed-off-by: Tirthendu Sarkar <tirthendu.sarkar@...el.com>
Tested-by: Chandan Kumar Rout <chandanx.rout@...el.com> (A Contingent Worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
---
 drivers/net/ethernet/intel/i40e/i40e_ethtool.c |  7 +++++++
 drivers/net/ethernet/intel/i40e/i40e_main.c    | 12 +++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
index 4934ff58332c..afc4fa8c66af 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
@@ -5402,6 +5402,13 @@ static int i40e_set_priv_flags(struct net_device *dev, u32 flags)
 		return -EOPNOTSUPP;
 	}
 
+	if ((changed_flags & I40E_FLAG_LEGACY_RX) &&
+	    I40E_2K_TOO_SMALL_WITH_PADDING) {
+		dev_warn(&pf->pdev->dev,
+			 "2k Rx buffer is too small to fit standard MTU and skb_shared_info\n");
+		return -EOPNOTSUPP;
+	}
+
 	if ((changed_flags & new_flags &
 	     I40E_FLAG_LINK_DOWN_ON_CLOSE_ENABLED) &&
 	    (new_flags & I40E_FLAG_MFP_ENABLED))
diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index d375d7940308..e8cf5644bf10 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
@@ -2903,7 +2903,7 @@ static void i40e_sync_filters_subtask(struct i40e_pf *pf)
 static u16 i40e_calculate_vsi_rx_buf_len(struct i40e_vsi *vsi)
 {
 	if (!vsi->netdev || (vsi->back->flags & I40E_FLAG_LEGACY_RX))
-		return I40E_RXBUFFER_2048;
+		return SKB_WITH_OVERHEAD(I40E_RXBUFFER_2048);
 
 	return PAGE_SIZE < 8192 ? I40E_RXBUFFER_3072 : I40E_RXBUFFER_2048;
 }
@@ -3661,10 +3661,16 @@ static int i40e_configure_rx_ring(struct i40e_ring *ring)
 	}
 
 	/* configure Rx buffer alignment */
-	if (!vsi->netdev || (vsi->back->flags & I40E_FLAG_LEGACY_RX))
+	if (!vsi->netdev || (vsi->back->flags & I40E_FLAG_LEGACY_RX)) {
+		if (I40E_2K_TOO_SMALL_WITH_PADDING) {
+			dev_info(&vsi->back->pdev->dev,
+				 "2k Rx buffer is too small to fit standard MTU and skb_shared_info\n");
+			return -EOPNOTSUPP;
+		}
 		clear_ring_build_skb_enabled(ring);
-	else
+	} else {
 		set_ring_build_skb_enabled(ring);
+	}
 
 	ring->rx_offset = i40e_rx_offset(ring);
 
-- 
2.38.1