Commit 986ef95e authored by Sagi Grimberg's avatar Sagi Grimberg Committed by Doug Ledford

IB/mlx5: Expose correct max_sge_rd limit

mlx5 devices (Connect-IB, ConnectX-4, ConnectX-4-LX) has a limitation
where rdma read work queue entries cannot exceed 512 bytes.
A rdma_read wqe needs to fit in 512 bytes:
- wqe control segment (16 bytes)
- rdma segment (16 bytes)
- scatter elements (16 bytes each)

So max_sge_rd should be: (512 - 16 - 16) / 16 = 30.

Cc: linux-stable@vger.kernel.org
Reported-by: default avatarChristoph Hellwig <hch@lst.de>
Tested-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarSagi Grimberg <sagig@grimberg.me>
Signed-off-by: default avatarLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
parent 32cc92c7
......@@ -530,7 +530,7 @@ static int mlx5_ib_query_device(struct ib_device *ibdev,
sizeof(struct mlx5_wqe_ctrl_seg)) /
sizeof(struct mlx5_wqe_data_seg);
props->max_sge = min(max_rq_sg, max_sq_sg);
props->max_sge_rd = props->max_sge;
props->max_sge_rd = MLX5_MAX_SGE_RD;
props->max_cq = 1 << MLX5_CAP_GEN(mdev, log_max_cq);
props->max_cqe = (1 << MLX5_CAP_GEN(mdev, log_max_cq_sz)) - 1;
props->max_mr = 1 << MLX5_CAP_GEN(mdev, log_max_mkey);
......
......@@ -392,6 +392,17 @@ enum {
MLX5_CAP_OFF_CMDIF_CSUM = 46,
};
enum {
/*
* Max wqe size for rdma read is 512 bytes, so this
* limits our max_sge_rd as the wqe needs to fit:
* - ctrl segment (16 bytes)
* - rdma segment (16 bytes)
* - scatter elements (16 bytes each)
*/
MLX5_MAX_SGE_RD = (512 - 16 - 16) / 16
};
struct mlx5_inbox_hdr {
__be16 opcode;
u8 rsvd[4];
......
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