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-rw-r--r--drivers/net/cxgb4vf/t4vf_hw.c11
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 */
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