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

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Date:   Mon,  6 Mar 2023 13:08:16 -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 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 1664 (2k - 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 8320.

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_main.c | 2 +-
 drivers/net/ethernet/intel/i40e/i40e_txrx.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
index d375d7940308..49e6cd1ef6cd 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 I40E_RXBUFFER_1664;
 
 	return PAGE_SIZE < 8192 ? I40E_RXBUFFER_3072 : I40E_RXBUFFER_2048;
 }
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
index 768290dc6f48..1382efb43ffd 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
@@ -97,6 +97,7 @@ enum i40e_dyn_idx_t {
 /* Supported Rx Buffer Sizes (a multiple of 128) */
 #define I40E_RXBUFFER_256   256
 #define I40E_RXBUFFER_1536  1536  /* 128B aligned standard Ethernet frame */
+#define I40E_RXBUFFER_1664  1664  /* For legacy Rx with tailroom for frags */
 #define I40E_RXBUFFER_2048  2048
 #define I40E_RXBUFFER_3072  3072  /* Used for large frames w/ padding */
 #define I40E_MAX_RXBUFFER   9728  /* largest size for single descriptor */
-- 
2.38.1