Be more like the BGE driver. Ensure that at least 16 TX descriptors are

kept unused in the ring.  This check should probably be moved up to
bce_start_locked at some point, as it'll make the loop up there slightly
more efficient, and will eliminate a costly set of busdma operations when
the ring is full.  But this works for now.

This makes all of my UDP torture tests work.  I'll cautiously say that
it might even work for other users now.  Feedback is appreciated.

1 files changed, 11 insertions, 8 deletions

diff --git a/sys/dev/bce/if_bce.c b/sys/dev/bce/if_bce.c
index 0eacbe2..cefd7f8 100644
--- a/sys/dev/bce/if_bce.c
+++ b/sys/dev/bce/if_bce.c
@@ -4549,13 +4549,6 @@ bce_tx_encap(struct bce_softc *sc, struct mbuf **m_head)
 	chain_prod = TX_CHAIN_IDX(prod);
 	map = sc->tx_mbuf_map[chain_prod];
 
-	/*
-	 * XXX This should be handled higher up.
-	 */
-	if ((USABLE_TX_BD - sc->used_tx_bd - BCE_TX_SLACK_SPACE) <= 0) {
-		return (ENOBUFS);
-	}
-
 	/* Map the mbuf into our DMA address space. */
 	error = bus_dmamap_load_mbuf_sg(sc->tx_mbuf_tag, map, m0,
 	    segs, &nsegs, BUS_DMA_NOWAIT);
@@ -4596,6 +4589,16 @@ bce_tx_encap(struct bce_softc *sc, struct mbuf **m_head)
 		return (error);
 	}
 
+	/*
+	 * The chip seems to require that at least 16 descriptors be kept
+	 * empty at all times.  Make sure we honor that.
+	 * XXX Would it be faster to assume worst case scenario for nsegs
+	 * and do this calculation higher up?
+	 */
+	if (nsegs > (USABLE_TX_BD - sc->used_tx_bd - BCE_TX_SLACK_SPACE)) {
+		bus_dmamap_unload(sc->tx_mbuf_tag, map);
+		return (ENOBUFS);
+	}
 
 	/* prod points to an empty tx_bd at this point. */
 	prod_bseq  = sc->tx_prod_bseq;
@@ -4701,7 +4704,7 @@ bce_start_locked(struct ifnet *ifp)
 		__FUNCTION__, tx_prod, tx_chain_prod, sc->tx_prod_bseq);
 
 	/* Keep adding entries while there is space in the ring. */
-	while (!IFQ_DRV_IS_EMPTY(&ifp->if_snd)) {
+	while (sc->tx_mbuf_ptr[tx_chain_prod] == NULL) {
 
 		/* Check for any frames to send. */
 		IFQ_DRV_DEQUEUE(&ifp->if_snd, m_head);