IB/mthca: correct log2 calculation

Fix thinko in rd_atomic calculation: ffs(x) - 1 does not find the next
power of 2 -- it should be fls(x - 1).

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 6 insertions, 11 deletions

diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c
index c5c3d0edbbf5..84056a8b794e 100644
--- a/drivers/infiniband/hw/mthca/mthca_qp.c
+++ b/drivers/infiniband/hw/mthca/mthca_qp.c
@@ -728,9 +728,9 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask)
         }
 
         if (attr_mask & IB_QP_MAX_QP_RD_ATOMIC) {
-                qp_context->params1 |= cpu_to_be32(min(attr->max_rd_atomic ?
-                                                       ffs(attr->max_rd_atomic) - 1 : 0,
-                                                       7) << 21);
+                if (attr->max_rd_atomic)
+                        qp_context->params1 |=
+                                cpu_to_be32(fls(attr->max_rd_atomic - 1) << 21);
                 qp_param->opt_param_mask |= cpu_to_be32(MTHCA_QP_OPTPAR_SRA_MAX);
         }
 
@@ -769,8 +769,6 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask)
         }
 
         if (attr_mask & IB_QP_MAX_DEST_RD_ATOMIC) {
-                u8 rra_max;
-
                 if (qp->resp_depth && !attr->max_dest_rd_atomic) {
                         /*
                          * Lowering our responder resources to zero.
@@ -798,13 +796,10 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask)
                                                                 MTHCA_QP_OPTPAR_RAE);
                 }
 
-                for (rra_max = 0;
-                     1 << rra_max < attr->max_dest_rd_atomic &&
-                             rra_max < dev->qp_table.rdb_shift;
-                     ++rra_max)
-                        ; /* nothing */
+                if (attr->max_dest_rd_atomic)
+                        qp_context->params2 |=
+                                cpu_to_be32(fls(attr->max_dest_rd_atomic - 1) << 21);
 
-                qp_context->params2      |= cpu_to_be32(rra_max << 21);
                 qp_param->opt_param_mask |= cpu_to_be32(MTHCA_QP_OPTPAR_RRA_MAX);
 
                 qp->resp_depth = attr->max_dest_rd_atomic;