[PATCH 4.4 095/163] IB/mlx5: Expose correct max_sge_rd limit

Greg Kroah-Hartman
2016-05-03T01:31:26Z

From: Sagi Grimberg <sagi@grimberg.me>

commit 986ef95ecdd3eb6fa29433e68faa94c7624083be upstream.

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.

Reported-by: Christoph Hellwig <hch@lst.de>
Tested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagig@grimberg.me>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/infiniband/hw/mlx5/main.c | 2 +-
include/linux/mlx5/device.h | 11 +++++++++++
2 files changed, 12 insertions(+), 1 deletion(-)

--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -273,7 +273,7 @@ static int mlx5_ib_query_device(struct i
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);
--- a/include/linux/mlx5/device.h
+++ b/include/linux/mlx5/device.h
@@ -334,6 +334,17 @@ 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];