netdev - [net-next 02/15] net/mlx5e: Add headroom only to the first fragment in legacy RQ

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Date:   Thu, 17 Mar 2022 11:54:11 -0700
From:   Saeed Mahameed <saeed@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Maxim Mikityanskiy <maximmi@...dia.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: [net-next 02/15] net/mlx5e: Add headroom only to the first fragment in legacy RQ

From: Maxim Mikityanskiy <maximmi@...dia.com>

Currently, rq->buff.headroom is applied to all fragments in legacy RQ.
In the linear mode, there is a non-zero headroom, but there is only one
fragment per packet. In the non-linear mode, the headroom is zero.

This commit changes the logic to apply the headroom only to the first
fragment. The current behavior remains the same for both linear and
non-linear modes. However, it allows the next commit to enable headroom
for the non-linear mode, which will be applied only to the first
fragment.

Signed-off-by: Maxim Mikityanskiy <maximmi@...dia.com>
Reviewed-by: Tariq Toukan <tariqt@...dia.com>
Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 074a44b281b6..6eda906342c0 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -373,12 +373,15 @@ static int mlx5e_alloc_rx_wqe(struct mlx5e_rq *rq, struct mlx5e_rx_wqe_cyc *wqe,
 	int i;
 
 	for (i = 0; i < rq->wqe.info.num_frags; i++, frag++) {
+		u16 headroom;
+
 		err = mlx5e_get_rx_frag(rq, frag);
 		if (unlikely(err))
 			goto free_frags;
 
+		headroom = i == 0 ? rq->buff.headroom : 0;
 		wqe->data[i].addr = cpu_to_be64(frag->di->addr +
-						frag->offset + rq->buff.headroom);
+						frag->offset + headroom);
 	}
 
 	return 0;
-- 
2.35.1