IB/mthca: Fix max_sge value returned by query_device
The mthca driver returns the maximum number of scatter/gather entries
returned by the firmware as the max_sge value when device properties
are queried. However, the firmware also reports a limit on the
maximum descriptor size allowed, and because mthca takes into account
the worst case send request overhead when checking whether to allow a
QP to be created, the largest number of scatter/gather entries that
can be used with mthca may be limited by the maximum descriptor size
rather than just by the actual s/g entry limit.
This means that applications cannot actually create QPs with
max_send_sge equal to the limit returned by ib_query_device(). Fix
this by checking if the maximum descriptor size imposes a lower limit
and if so returning that lower limit.
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/mthca/mthca_main.c b/drivers/infiniband/hw/mthca/mthca_main.c
index 9ebadd6..200cf13f 100644
--- a/drivers/infiniband/hw/mthca/mthca_main.c
+++ b/drivers/infiniband/hw/mthca/mthca_main.c
@@ -45,6 +45,7 @@
#include "mthca_cmd.h"
#include "mthca_profile.h"
#include "mthca_memfree.h"
+#include "mthca_wqe.h"
MODULE_AUTHOR("Roland Dreier");
MODULE_DESCRIPTION("Mellanox InfiniBand HCA low-level driver");
@@ -200,7 +201,18 @@
mdev->limits.gid_table_len = dev_lim->max_gids;
mdev->limits.pkey_table_len = dev_lim->max_pkeys;
mdev->limits.local_ca_ack_delay = dev_lim->local_ca_ack_delay;
- mdev->limits.max_sg = dev_lim->max_sg;
+ /*
+ * Need to allow for worst case send WQE overhead and check
+ * whether max_desc_sz imposes a lower limit than max_sg; UD
+ * send has the biggest overhead.
+ */
+ mdev->limits.max_sg = min_t(int, dev_lim->max_sg,
+ (dev_lim->max_desc_sz -
+ sizeof (struct mthca_next_seg) -
+ (mthca_is_memfree(mdev) ?
+ sizeof (struct mthca_arbel_ud_seg) :
+ sizeof (struct mthca_tavor_ud_seg))) /
+ sizeof (struct mthca_data_seg));
mdev->limits.max_wqes = dev_lim->max_qp_sz;
mdev->limits.max_qp_init_rdma = dev_lim->max_requester_per_qp;
mdev->limits.reserved_qps = dev_lim->reserved_qps;