rdma core: Add rdma_rw_mr_payload()

The amount of payload per MR depends on device capabilities and
the memory registration mode in use. The new rdma_rw API hides both,
making it difficult for ULPs to determine how large their transport
send queues need to be.

Expose the MR payload information via a new API.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 26 insertions, 0 deletions

diff --git a/drivers/infiniband/core/rw.c b/drivers/infiniband/core/rw.c
index dbfd854c32c9..6ca607e8e293 100644
--- a/drivers/infiniband/core/rw.c
+++ b/drivers/infiniband/core/rw.c
@@ -643,6 +643,30 @@ void rdma_rw_ctx_destroy_signature(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
 }
 EXPORT_SYMBOL(rdma_rw_ctx_destroy_signature);
 
+/**
+ * rdma_rw_mr_factor - return number of MRs required for a payload
+ * @device:     device handling the connection
+ * @port_num:   port num to which the connection is bound
+ * @maxpages:   maximum payload pages per rdma_rw_ctx
+ *
+ * Returns the number of MRs the device requires to move @maxpayload
+ * bytes. The returned value is used during transport creation to
+ * compute max_rdma_ctxts and the size of the transport's Send and
+ * Send Completion Queues.
+ */
+unsigned int rdma_rw_mr_factor(struct ib_device *device, u8 port_num,
+                               unsigned int maxpages)
+{
+        unsigned int mr_pages;
+
+        if (rdma_rw_can_use_mr(device, port_num))
+                mr_pages = rdma_rw_fr_page_list_len(device);
+        else
+                mr_pages = device->attrs.max_sge_rd;
+        return DIV_ROUND_UP(maxpages, mr_pages);
+}
+EXPORT_SYMBOL(rdma_rw_mr_factor);
+
 void rdma_rw_init_qp(struct ib_device *dev, struct ib_qp_init_attr *attr)
 {
         u32 factor;
diff --git a/include/rdma/rw.h b/include/rdma/rw.h
index 377d865e506d..a3cbbc7b6417 100644
--- a/include/rdma/rw.h
+++ b/include/rdma/rw.h
@@ -81,6 +81,8 @@ struct ib_send_wr *rdma_rw_ctx_wrs(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
 int rdma_rw_ctx_post(struct rdma_rw_ctx *ctx, struct ib_qp *qp, u8 port_num,
                 struct ib_cqe *cqe, struct ib_send_wr *chain_wr);
 
+unsigned int rdma_rw_mr_factor(struct ib_device *device, u8 port_num,
+                unsigned int maxpages);
 void rdma_rw_init_qp(struct ib_device *dev, struct ib_qp_init_attr *attr);
 int rdma_rw_init_mrs(struct ib_qp *qp, struct ib_qp_init_attr *attr);
 void rdma_rw_cleanup_mrs(struct ib_qp *qp);