staging/rdma/hfi1: Fix xmit discard error weight

Count only the errors that apply to xmit discards.  Update
the comment to better explain the limitations of the count.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

diff --git a/drivers/staging/rdma/hfi1/chip.c b/drivers/staging/rdma/hfi1/chip.c
index 93bf465..6e44d52 100644 (file)
--- a/drivers/staging/rdma/hfi1/chip.c
+++ b/drivers/staging/rdma/hfi1/chip.c
@@ -5566,12 +5566,28 @@ static void handle_send_egress_err_info(struct hfi1_devdata *dd,
                int weight, i;
 
                /*
-                * Count all, in case multiple bits are set.  Reminder:
-                * since there is only one info register for many sources,
-                * these may be attributed to the wrong VL if they occur
-                * too close together.
+                * Count all applicable bits as individual errors and
+                * attribute them to the packet that triggered this handler.
+                * This may not be completely accurate due to limitations
+                * on the available hardware error information.  There is
+                * a single information register and any number of error
+                * packets may have occurred and contributed to it before
+                * this routine is called.  This means that:
+                * a) If multiple packets with the same error occur before
+                *    this routine is called, earlier packets are missed.
+                *    There is only a single bit for each error type.
+                * b) Errors may not be attributed to the correct VL.
+                *    The driver is attributing all bits in the info register
+                *    to the packet that triggered this call, but bits
+                *    could be an accumulation of different packets with
+                *    different VLs.
+                * c) A single error packet may have multiple counts attached
+                *    to it.  There is no way for the driver to know if
+                *    multiple bits set in the info register are due to a
+                *    single packet or multiple packets.  The driver assumes
+                *    multiple packets.
                 */
-               weight = hweight64(info);
+               weight = hweight64(info & PORT_DISCARD_EGRESS_ERRS);
                for (i = 0; i < weight; i++) {
                        __count_port_discards(ppd);
                        if (vl >= 0 && vl < TXE_NUM_DATA_VL)