mlx4: Expose correct max_sge_rd limit
mlx4 devices (ConnectX-2, ConnectX-3) 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.
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
diff --git a/include/linux/mlx4/device.h b/include/linux/mlx4/device.h
index 7501626..d3133be 100644
--- a/include/linux/mlx4/device.h
+++ b/include/linux/mlx4/device.h
@@ -427,6 +427,17 @@
};
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)
+ */
+ MLX4_MAX_SGE_RD = (512 - 16 - 16) / 16
+};
+
+enum {
MLX4_DEV_PMC_SUBTYPE_GUID_INFO = 0x14,
MLX4_DEV_PMC_SUBTYPE_PORT_INFO = 0x15,
MLX4_DEV_PMC_SUBTYPE_PKEY_TABLE = 0x16,