o In order to reduce bug and code duplication fold handling of NICs

  requiring DC_TX_ALIGN or DC_TX_COALESCE, which was previously done
  in dc_start_locked(), into dc_encap().
o In dc_encap():
  - If m_defrag() fails just drop the packet like other NIC drivers
    do. This should only happen when there's a mbuf shortage, in which
    case it was possible to end up with an IFQ full of packets which
    couldn't be processed as they couldn't be defragmented as they
    were taking up all the mbufs themselves. This includes adjusting
    dc_start_locked() to not trying to prepend the mbuf (chain) if
    dc_encap() has freed it.
  - Likewise, if bus_dmamap_load_mbuf() fails as dc_dma_map_txbuf()
    failed, free the mbuf possibly allocated by the above call to
    m_defrag() and drop the packet.
o In dc_txeof():
  - Don't clear IFF_DRV_OACTIVE unless there are at least 6 free TX
    descriptors. Further down the road dc_encap() will bail if there
    are only 5 or fewer free TX descriptors, causing dc_start_locked()
    to abort and prepend the dequeued mbuf again so it makes no sense
    to pretend we could process mbufs again when in fact we won't.
    While at it replace this magic 5 with a macro DC_TX_LIST_RSVD.
  - Just always assign idx to sc->dc_cdata.dc_tx_cons; it doesn't
    make much sense to exclude the idx == sc->dc_cdata.dc_tx_cons
    case.
o In dc_dma_map_txbuf() there's no need to set sc->dc_cdata.dc_tx_err
  to error if the latter is != 0, bus_dmamap_load_mbuf() already
  returns the same error value in that case anyway.
o For less overhead, convert to use bus_dmamap_load_mbuf_sg() for
  loading RX buffers.
o Remove some banal and/or outdated comments.

Approved by:	re (kensmith)
MFC after:	1 week

2 files changed, 31 insertions, 69 deletions

diff --git a/sys/dev/dc/if_dc.c b/sys/dev/dc/if_dc.c
index 42474dc..e3d9465 100644
--- a/sys/dev/dc/if_dc.c
+++ b/sys/dev/dc/if_dc.c
@@ -294,7 +294,6 @@ static void dc_decode_leaf_sym(struct dc_softc *, struct dc_eblock_sym *);
 static void dc_apply_fixup(struct dc_softc *, int);
 
 static void dc_dma_map_txbuf(void *, bus_dma_segment_t *, int, bus_size_t, int);
-static void dc_dma_map_rxbuf(void *, bus_dma_segment_t *, int, bus_size_t, int);
 
 #ifdef DC_USEIOSPACE
 #define DC_RES			SYS_RES_IOPORT
@@ -2424,29 +2423,6 @@ dc_list_rx_init(struct dc_softc *sc)
 	return (0);
 }
 
-static void
-dc_dma_map_rxbuf(arg, segs, nseg, mapsize, error)
-	void *arg;
-	bus_dma_segment_t *segs;
-	int nseg;
-	bus_size_t mapsize;
-	int error;
-{
-	struct dc_softc *sc;
-	struct dc_desc *c;
-
-	sc = arg;
-	c = &sc->dc_ldata->dc_rx_list[sc->dc_cdata.dc_rx_cur];
-	if (error) {
-		sc->dc_cdata.dc_rx_err = error;
-		return;
-	}
-
-	KASSERT(nseg == 1, ("wrong number of segments, should be 1"));
-	sc->dc_cdata.dc_rx_err = 0;
-	c->dc_data = htole32(segs->ds_addr);
-}
-
 /*
  * Initialize an RX descriptor and attach an MBUF cluster.
  */
@@ -2455,7 +2431,8 @@ dc_newbuf(struct dc_softc *sc, int i, int alloc)
 {
 	struct mbuf *m_new;
 	bus_dmamap_t tmp;
-	int error;
+	bus_dma_segment_t segs[1];
+	int error, nseg;
 
 	if (alloc) {
 		m_new = m_getcl(M_DONTWAIT, MT_DATA, M_PKTHDR);
@@ -2478,17 +2455,14 @@ dc_newbuf(struct dc_softc *sc, int i, int alloc)
 
 	/* No need to remap the mbuf if we're reusing it. */
 	if (alloc) {
-		sc->dc_cdata.dc_rx_cur = i;
-		error = bus_dmamap_load_mbuf(sc->dc_mtag, sc->dc_sparemap,
-		    m_new, dc_dma_map_rxbuf, sc, 0);
+		error = bus_dmamap_load_mbuf_sg(sc->dc_mtag, sc->dc_sparemap,
+		    m_new, segs, &nseg, 0);
+		KASSERT(nseg == 1, ("wrong number of segments, should be 1"));
 		if (error) {
 			m_freem(m_new);
 			return (error);
 		}
-		if (sc->dc_cdata.dc_rx_err != 0) {
-			m_freem(m_new);
-			return (sc->dc_cdata.dc_rx_err);
-		}
+		sc->dc_ldata->dc_rx_list[i].dc_data = htole32(segs->ds_addr);
 		bus_dmamap_unload(sc->dc_mtag, sc->dc_cdata.dc_rx_map[i]);
 		tmp = sc->dc_cdata.dc_rx_map[i];
 		sc->dc_cdata.dc_rx_map[i] = sc->dc_sparemap;
@@ -2865,12 +2839,11 @@ dc_txeof(struct dc_softc *sc)
 		sc->dc_cdata.dc_tx_cnt--;
 		DC_INC(idx, DC_TX_LIST_CNT);
 	}
+	sc->dc_cdata.dc_tx_cons = idx;
 
-	if (idx != sc->dc_cdata.dc_tx_cons) {
-	    	/* Some buffers have been freed. */
-		sc->dc_cdata.dc_tx_cons = idx;
+	if (DC_TX_LIST_CNT - sc->dc_cdata.dc_tx_cnt > DC_TX_LIST_RSVD)
 		ifp->if_drv_flags &= ~IFF_DRV_OACTIVE;
-	}
+
 	if (sc->dc_cdata.dc_tx_cnt == 0)
 		sc->dc_wdog_timer = 0;
 }
@@ -3161,10 +3134,8 @@ dc_dma_map_txbuf(arg, segs, nseg, mapsize, error)
 	int cur, first, frag, i;
 
 	sc = arg;
-	if (error) {
-		sc->dc_cdata.dc_tx_err = error;
+	if (error)
 		return;
-	}
 
 	first = cur = frag = sc->dc_cdata.dc_tx_prod;
 	for (i = 0; i < nseg; i++) {
@@ -3217,7 +3188,7 @@ dc_encap(struct dc_softc *sc, struct mbuf **m_head)
 	/*
 	 * If there's no way we can send any packets, return now.
 	 */
-	if (DC_TX_LIST_CNT - sc->dc_cdata.dc_tx_cnt < 6)
+	if (DC_TX_LIST_CNT - sc->dc_cdata.dc_tx_cnt <= DC_TX_LIST_RSVD)
 		return (ENOBUFS);
 
 	/*
@@ -3229,27 +3200,30 @@ dc_encap(struct dc_softc *sc, struct mbuf **m_head)
 	for (m = *m_head; m != NULL; m = m->m_next)
 		chainlen++;
 
-	if ((chainlen > DC_TX_LIST_CNT / 4) ||
-	    ((DC_TX_LIST_CNT - (chainlen + sc->dc_cdata.dc_tx_cnt)) < 6)) {
+	m = NULL;
+	if ((sc->dc_flags & DC_TX_COALESCE && ((*m_head)->m_next != NULL ||
+	    sc->dc_flags & DC_TX_ALIGN)) || (chainlen > DC_TX_LIST_CNT / 4) ||
+	    (DC_TX_LIST_CNT - (chainlen + sc->dc_cdata.dc_tx_cnt) <=
+	    DC_TX_LIST_RSVD)) {
 		m = m_defrag(*m_head, M_DONTWAIT);
-		if (m == NULL)
+		if (m == NULL) {
+			m_freem(*m_head);
+			*m_head = NULL;
 			return (ENOBUFS);
+		}
 		*m_head = m;
 	}
-
-	/*
-	 * Start packing the mbufs in this chain into
-	 * the fragment pointers. Stop when we run out
-	 * of fragments or hit the end of the mbuf chain.
-	 */
 	idx = sc->dc_cdata.dc_tx_prod;
 	sc->dc_cdata.dc_tx_mapping = *m_head;
 	error = bus_dmamap_load_mbuf(sc->dc_mtag, sc->dc_cdata.dc_tx_map[idx],
 	    *m_head, dc_dma_map_txbuf, sc, 0);
-	if (error)
-		return (error);
-	if (sc->dc_cdata.dc_tx_err != 0)
-		return (sc->dc_cdata.dc_tx_err);
+	if (error != 0 || sc->dc_cdata.dc_tx_err != 0) {
+		if (m != NULL) {
+			m_freem(m);
+			*m_head = NULL;
+		}
+		return (error != 0 ? error : sc->dc_cdata.dc_tx_err);
+	}
 	bus_dmamap_sync(sc->dc_mtag, sc->dc_cdata.dc_tx_map[idx],
 	    BUS_DMASYNC_PREWRITE);
 	bus_dmamap_sync(sc->dc_ltag, sc->dc_lmap,
@@ -3279,7 +3253,7 @@ static void
 dc_start_locked(struct ifnet *ifp)
 {
 	struct dc_softc *sc;
-	struct mbuf *m_head = NULL, *m;
+	struct mbuf *m_head = NULL;
 	unsigned int queued = 0;
 	int idx;
 
@@ -3300,20 +3274,9 @@ dc_start_locked(struct ifnet *ifp)
 		if (m_head == NULL)
 			break;
 
-		if (sc->dc_flags & DC_TX_COALESCE &&
-		    (m_head->m_next != NULL ||
-		     sc->dc_flags & DC_TX_ALIGN)) {
-			m = m_defrag(m_head, M_DONTWAIT);
-			if (m == NULL) {
-				IFQ_DRV_PREPEND(&ifp->if_snd, m_head);
-				ifp->if_drv_flags |= IFF_DRV_OACTIVE;
-				break;
-			} else {
-				m_head = m;
-			}
-		}
-
 		if (dc_encap(sc, &m_head)) {
+			if (m_head == NULL)
+				break;
 			IFQ_DRV_PREPEND(&ifp->if_snd, m_head);
 			ifp->if_drv_flags |= IFF_DRV_OACTIVE;
 			break;
diff --git a/sys/dev/dc/if_dcreg.h b/sys/dev/dc/if_dcreg.h
index 3ab930e..9417a13 100644
--- a/sys/dev/dc/if_dcreg.h
+++ b/sys/dev/dc/if_dcreg.h
@@ -461,6 +461,7 @@ struct dc_desc {
 #define DC_RX_LIST_CNT		64
 #endif
 #define DC_TX_LIST_CNT		256
+#define DC_TX_LIST_RSVD		5
 #define DC_MIN_FRAMELEN		60
 #define DC_RXLEN		1536
 
@@ -496,8 +497,6 @@ struct dc_chain_data {
 	int			dc_tx_prod;
 	int			dc_tx_cons;
 	int			dc_tx_cnt;
-	int			dc_rx_err;
-	int			dc_rx_cur;
 	int			dc_rx_prod;
 };