1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/net/cxgb4vf/t4vf_hw.c b/drivers/net/cxgb4vf/t4vf_hw.c
index e4bec78c8e3f..0f51c80475ce 100644
--- a/drivers/net/cxgb4vf/t4vf_hw.c
+++ b/drivers/net/cxgb4vf/t4vf_hw.c
@@ -147,9 +147,20 @@ int t4vf_wr_mbox_core(struct adapter *adapter, const void *cmd, int size,
         /*
          * Write the command array into the Mailbox Data register array and
          * transfer ownership of the mailbox to the firmware.
+         *
+         * For the VFs, the Mailbox Data "registers" are actually backed by
+         * T4's "MA" interface rather than PL Registers (as is the case for
+         * the PFs).  Because these are in different coherency domains, the
+         * write to the VF's PL-register-backed Mailbox Control can race in
+         * front of the writes to the MA-backed VF Mailbox Data "registers".
+         * So we need to do a read-back on at least one byte of the VF Mailbox
+         * Data registers before doing the write to the VF Mailbox Control
+         * register.
          */
         for (i = 0, p = cmd; i < size; i += 8)
                 t4_write_reg64(adapter, mbox_data + i, be64_to_cpu(*p++));
+        t4_read_reg(adapter, mbox_data);         /* flush write */
+
         t4_write_reg(adapter, mbox_ctl,
                      MBMSGVALID | MBOWNER(MBOX_OWNER_FW));
         t4_read_reg(adapter, mbox_ctl);          /* flush write */