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>

diff --git a/drivers/infiniband/hw/ipath/ipath_iba6120.c b/drivers/infiniband/hw/ipath/ipath_iba6120.c
index a324c6f7aeba11524dc56f7f6a28fb7abd64f357..d43f0b3a43fefe96d6e8e7d3566dfdbf82a38d83 100644 (file)
--- 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);