myx requires the driver pad short ethernet frames to 60 bytes by

adding a descriptor pointing at zeroed bytes onto the end of transmit
chains. i was accounting for this extra descriptor when i was
completing the chain, but not when i was setting this up.  this
meant the number of free descriptors kept growing until it overflowed.
at this point the check for space in the ring failed and packets
no longer flowed.

this counts the pad descriptor in the tx chain setup too.

ok deraadt@

1 files changed, 2 insertions, 3 deletions

diff --git a/sys/dev/pci/if_myx.c b/sys/dev/pci/if_myx.c
index 8a1186d4221..f15fe82af59 100644
--- a/sys/dev/pci/if_myx.c
+++ b/sys/dev/pci/if_myx.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if_myx.c,v 1.28 2011/06/23 04:09:08 dlg Exp $	*/
+/*	$OpenBSD: if_myx.c,v 1.29 2011/08/08 01:30:25 dlg Exp $	*/
 
 /*
  * Copyright (c) 2007 Reyk Floeter <reyk@openbsd.org>
@@ -1426,8 +1426,6 @@ myx_start(struct ifnet *ifp)
 		bus_dmamap_sync(sc->sc_dmat, map, 0,
 		    map->dm_mapsize, BUS_DMASYNC_POSTWRITE);
 
-		sc->sc_tx_free -= map->dm_nsegs;
-
 		myx_buf_put(&sc->sc_tx_buf_list, mb);
 
 		flags = MYXTXD_FLAGS_NO_TSO;
@@ -1470,6 +1468,7 @@ myx_start(struct ifnet *ifp)
 		myx_write(sc, offset + idx * sizeof(txd),
 		    &txd, sizeof(txd));
 
+		sc->sc_tx_free -= i;
 		idx += i;
 		idx %= sc->sc_tx_ring_count;
 	}