IB/ipath: Better comment for rmb() in ipath_intr()

An internal code review found the comment here lacking -- update it with 
more specifics of how and why the rmb() is there.

Signed-off-by: Arthur Jones <arthur.jones@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_intr.c b/drivers/infiniband/hw/ipath/ipath_intr.c
index eac2e9c5528..4795cb895f8 100644
--- a/drivers/infiniband/hw/ipath/ipath_intr.c
+++ b/drivers/infiniband/hw/ipath/ipath_intr.c
@@ -954,7 +954,15 @@ static void handle_urcv(struct ipath_devdata *dd, u32 istat)
         int i;
         int rcvdint = 0;
 
-        /* test_bit below needs this... */
+        /*
+         * test_and_clear_bit(IPATH_PORT_WAITING_RCV) and
+         * test_and_clear_bit(IPATH_PORT_WAITING_URG) below
+         * would both like timely updates of the bits so that
+         * we don't pass them by unnecessarily.  the rmb()
+         * here ensures that we see them promptly -- the
+         * corresponding wmb()'s are in ipath_poll_urgent()
+         * and ipath_poll_next()...
+         */
         rmb();
         portr = ((istat >> INFINIPATH_I_RCVAVAIL_SHIFT) &
                  dd->ipath_i_rcvavail_mask)