idpf: fix minor controlq issues

While we're here improving virtchnl we can include two minor fixes for
the lower level ctrlq flow.

This adds a memory barrier to idpf_post_rx_buffs before we update tail
on the controlq.  We should make sure our writes have had a chance to
finish before we tell HW it can touch them.

This also removes some defensive programming in idpf_ctrlq_recv. The
caller should not be using a num_q_msg value of zero or more than the
ring size and it's their responsibility to call functions sanely.

Tested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Author: atbrady-intel

drivers/net/ethernet/intel/idpf/idpf_controlq.c

@@ -516,6 +516,8 @@ int idpf_ctlq_post_rx_buffs(struct idpf_hw *hw, struct idpf_ctlq_info *cq,
 			/* Wrap to end of end ring since current ntp is 0 */
 			cq->next_to_post = cq->ring_size - 1;
 
+		dma_wmb();
+
 		wr32(hw, cq->reg.tail, cq->next_to_post);
 	}
 
@@ -546,11 +548,6 @@ int idpf_ctlq_recv(struct idpf_ctlq_info *cq, u16 *num_q_msg,
 	int err = 0;
 	u16 i;
 
-	if (*num_q_msg == 0)
-		return 0;
-	else if (*num_q_msg > cq->ring_size)
-		return -EBADR;
-
 	/* take the lock before we start messing with the ring */
 	mutex_lock(&cq->cq_lock);