iwm: use m_collapse() to defragment a mbuf chain

- Simplify defragmentation code.
- Use proper number of dma segments for data.

Approved by:	adrian (mentor)
Obtained from:	DragonFlyBSD (mostly)
Differential Revision:	https://reviews.freebsd.org/D4754

1 files changed, 6 insertions, 14 deletions

diff --git a/sys/dev/iwm/if_iwm.c b/sys/dev/iwm/if_iwm.c
index 874921f73006..73cccd996afd 100644
--- a/sys/dev/iwm/if_iwm.c
+++ b/sys/dev/iwm/if_iwm.c
@@ -956,7 +956,7 @@ iwm_alloc_tx_ring(struct iwm_softc *sc, struct iwm_tx_ring *ring, int qid)
 
 	error = bus_dma_tag_create(sc->sc_dmat, 1, 0,
 	    BUS_SPACE_MAXADDR_32BIT, BUS_SPACE_MAXADDR, NULL, NULL, MCLBYTES,
-            IWM_MAX_SCATTER - 1, MCLBYTES, 0, NULL, NULL, &ring->data_dmat);
+            IWM_MAX_SCATTER - 2, MCLBYTES, 0, NULL, NULL, &ring->data_dmat);
 	if (error != 0) {
 		device_printf(sc->sc_dev, "could not create TX buf DMA tag\n");
 		goto fail;
@@ -2778,23 +2778,15 @@ iwm_tx(struct iwm_softc *sc, struct mbuf *m, struct ieee80211_node *ni, int ac)
 			return error;
 		}
 		/* Too many DMA segments, linearize mbuf. */
-		MGETHDR(m1, M_NOWAIT, MT_DATA);
+		m1 = m_collapse(m, M_NOWAIT, IWM_MAX_SCATTER - 2);
 		if (m1 == NULL) {
+			device_printf(sc->sc_dev,
+			    "%s: could not defrag mbuf\n", __func__);
 			m_freem(m);
-			return ENOBUFS;
-		}
-		if (m->m_pkthdr.len > MHLEN) {
-			MCLGET(m1, M_NOWAIT);
-			if (!(m1->m_flags & M_EXT)) {
-				m_freem(m);
-				m_freem(m1);
-				return ENOBUFS;
-			}
+			return (ENOBUFS);
 		}
-		m_copydata(m, 0, m->m_pkthdr.len, mtod(m1, void *));
-		m1->m_pkthdr.len = m1->m_len = m->m_pkthdr.len;
-		m_freem(m);
 		m = m1;
+
 		error = bus_dmamap_load_mbuf_sg(ring->data_dmat, data->map, m,
 		    segs, &nsegs, BUS_DMA_NOWAIT);
 		if (error != 0) {