IB/ipath: Correctly describe workaround for TID write chip bug

This is a comment change, only, correcting the comment to match the
implemented workaround, rather than the original workaround, and
clarifying why it's needed.

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_iba6120.c b/drivers/infiniband/hw/ipath/ipath_iba6120.c
index a324c6f7aeba..d43f0b3a43fe 100644
--- a/drivers/infiniband/hw/ipath/ipath_iba6120.c
+++ b/drivers/infiniband/hw/ipath/ipath_iba6120.c
@@ -1143,11 +1143,14 @@ static void ipath_pe_put_tid(struct ipath_devdata *dd, u64 __iomem *tidptr,
                         pa |= 2 << 29;
         }
 
-        /* workaround chip bug 9437 by writing each TID twice
-         * and holding a spinlock around the writes, so they don't
-         * intermix with other TID (eager or expected) writes
-         * Unfortunately, this call can be done from interrupt level
-         * for the port 0 eager TIDs, so we have to use irqsave
+        /*
+         * Workaround chip bug 9437 by writing the scratch register
+         * before and after the TID, and with an io write barrier.
+         * We use a spinlock around the writes, so they can't intermix
+         * with other TID (eager or expected) writes (the chip bug
+         * is triggered by back to back TID writes). Unfortunately, this
+         * call can be done from interrupt level for the port 0 eager TIDs,
+         * so we have to use irqsave locks.
          */
         spin_lock_irqsave(&dd->ipath_tid_lock, flags);
         ipath_write_kreg(dd, dd->ipath_kregs->kr_scratch, 0xfeeddeaf);