Unlike most other controllers, NS DP83815/DP83816 controllers seem

to pad with 0xFF when it encounter short frames.  According to RFC
1042 the pad bytes should be 0x00.
Because manual padding consumes extra CPU cycles, introduce a new
tunable which controls the padding behavior. Turning this tunable
on will have driver pad manually but it's disabled by default. Users
can enable software padding by setting the following tunable to
non-zero value.

dev.sis.%d.manual_pad="1"

PR:	kern/35422 (patch not used)

2 files changed, 81 insertions, 10 deletions

diff --git a/sys/dev/sis/if_sis.c b/sys/dev/sis/if_sis.c
index ee12a9c..ceff6b8 100644
--- a/sys/dev/sis/if_sis.c
+++ b/sys/dev/sis/if_sis.c
@@ -73,6 +73,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/module.h>
 #include <sys/socket.h>
 #include <sys/sockio.h>
+#include <sys/sysctl.h>
 
 #include <net/if.h>
 #include <net/if_arp.h>
@@ -150,6 +151,7 @@ static int sis_rxeof(struct sis_softc *);
 static void sis_start(struct ifnet *);
 static void sis_startl(struct ifnet *);
 static void sis_stop(struct sis_softc *);
+static void sis_add_sysctls(struct sis_softc *);
 static void sis_watchdog(struct sis_softc *);
 
 
@@ -710,24 +712,24 @@ sis_miibus_statchg(device_t dev)
 	    (ifp->if_drv_flags & IFF_DRV_RUNNING) == 0)
 		return;
 
-	sc->sis_link = 0;
+	sc->sis_flags &= ~SIS_FLAG_LINK;
 	if ((mii->mii_media_status & (IFM_ACTIVE | IFM_AVALID)) ==
 	    (IFM_ACTIVE | IFM_AVALID)) {
 		switch (IFM_SUBTYPE(mii->mii_media_active)) {
 		case IFM_10_T:
-			sc->sis_link++;
 			CSR_WRITE_4(sc, SIS_TX_CFG, SIS_TXCFG_10);
+			sc->sis_flags |= SIS_FLAG_LINK;
 			break;
 		case IFM_100_TX:
-			sc->sis_link++;
 			CSR_WRITE_4(sc, SIS_TX_CFG, SIS_TXCFG_100);
+			sc->sis_flags |= SIS_FLAG_LINK;
 			break;
 		default:
 			break;
 		}
 	}
 
-	if (sc->sis_link == 0) {
+	if ((sc->sis_flags & SIS_FLAG_LINK) == 0) {
 		/*
 		 * Stopping MACs seem to reset SIS_TX_LISTPTR and
 		 * SIS_RX_LISTPTR which in turn requires resetting
@@ -1122,6 +1124,8 @@ sis_attach(device_t dev)
 		break;
 	}
 
+	sis_add_sysctls(sc);
+
 	/* Allocate DMA'able memory. */
 	if ((error = sis_dma_alloc(sc)) != 0)
 		goto fail;
@@ -1698,7 +1702,7 @@ sis_tick(void *xsc)
 	mii = device_get_softc(sc->sis_miibus);
 	mii_tick(mii);
 	sis_watchdog(sc);
-	if (sc->sis_link == 0)
+	if ((sc->sis_flags & SIS_FLAG_LINK) == 0)
 		sis_miibus_statchg(sc->sis_dev);
 	callout_reset(&sc->sis_stat_ch, hz,  sis_tick, sc);
 }
@@ -1829,9 +1833,41 @@ sis_encap(struct sis_softc *sc, struct mbuf **m_head)
 	bus_dma_segment_t	segs[SIS_MAXTXSEGS];
 	bus_dmamap_t		map;
 	int			error, i, frag, nsegs, prod;
+	int			padlen;
 
 	prod = sc->sis_tx_prod;
 	txd = &sc->sis_txdesc[prod];
+	if ((sc->sis_flags & SIS_FLAG_MANUAL_PAD) != 0 &&
+	    (*m_head)->m_pkthdr.len < SIS_MIN_FRAMELEN) {
+		m = *m_head;
+		padlen = SIS_MIN_FRAMELEN - m->m_pkthdr.len;
+		if (M_WRITABLE(m) == 0) {
+			/* Get a writable copy. */
+			m = m_dup(*m_head, M_DONTWAIT);
+			m_freem(*m_head);
+			if (m == NULL) {
+				*m_head = NULL;
+				return (ENOBUFS);
+			}
+			*m_head = m;
+		}
+		if (m->m_next != NULL || M_TRAILINGSPACE(m) < padlen) {
+			m = m_defrag(m, M_DONTWAIT);
+			if (m == NULL) {
+				m_freem(*m_head);
+				*m_head = NULL;
+				return (ENOBUFS);
+			}
+		}
+		/*
+		 * Manually pad short frames, and zero the pad space
+		 * to avoid leaking data.
+		 */
+		bzero(mtod(m, char *) + m->m_pkthdr.len, padlen);
+		m->m_pkthdr.len += padlen;
+		m->m_len = m->m_pkthdr.len;
+		*m_head = m;
+	}
 	error = bus_dmamap_load_mbuf_sg(sc->sis_tx_tag, txd->tx_dmamap,
 	    *m_head, segs, &nsegs, 0);
 	if (error == EFBIG) {
@@ -1918,7 +1954,7 @@ sis_startl(struct ifnet *ifp)
 	SIS_LOCK_ASSERT(sc);
 
 	if ((ifp->if_drv_flags & (IFF_DRV_RUNNING | IFF_DRV_OACTIVE)) !=
-	    IFF_DRV_RUNNING || sc->sis_link == 0)
+	    IFF_DRV_RUNNING || (sc->sis_flags & SIS_FLAG_LINK) == 0)
 		return;
 
 	for (queued = 0; !IFQ_DRV_IS_EMPTY(&ifp->if_snd) &&
@@ -2025,6 +2061,13 @@ sis_initl(struct sis_softc *sc)
 		return;
 	}
 
+	if (sc->sis_type == SIS_TYPE_83815 || sc->sis_type == SIS_TYPE_83816) {
+		if (sc->sis_manual_pad != 0)
+			sc->sis_flags |= SIS_FLAG_MANUAL_PAD;
+		else
+			sc->sis_flags &= ~SIS_FLAG_MANUAL_PAD;
+	}
+
 	/*
 	 * Short Cable Receive Errors (MP21.E)
 	 * also: Page 78 of the DP83815 data sheet (september 2002 version)
@@ -2125,7 +2168,7 @@ sis_initl(struct sis_softc *sc)
 	/* Clear MAC disable. */
 	SIS_CLRBIT(sc, SIS_CSR, SIS_CSR_TX_DISABLE | SIS_CSR_RX_DISABLE);
 
-	sc->sis_link = 0;
+	sc->sis_flags &= ~SIS_FLAG_LINK;
 	mii_mediachg(mii);
 
 	ifp->if_drv_flags |= IFF_DRV_RUNNING;
@@ -2148,7 +2191,6 @@ sis_ifmedia_upd(struct ifnet *ifp)
 
 	SIS_LOCK(sc);
 	mii = device_get_softc(sc->sis_miibus);
-	sc->sis_link = 0;
 	if (mii->mii_instance) {
 		struct mii_softc	*miisc;
 		LIST_FOREACH(miisc, &mii->mii_phys, mii_list)
@@ -2304,7 +2346,7 @@ sis_stop(struct sis_softc *sc)
 	CSR_WRITE_4(sc, SIS_TX_LISTPTR, 0);
 	CSR_WRITE_4(sc, SIS_RX_LISTPTR, 0);
 
-	sc->sis_link = 0;
+	sc->sis_flags &= ~SIS_FLAG_LINK;
 
 	/*
 	 * Free data in the RX lists.
@@ -2351,6 +2393,32 @@ sis_shutdown(device_t dev)
 	return (0);
 }
 
+static void
+sis_add_sysctls(struct sis_softc *sc)
+{
+	struct sysctl_ctx_list *ctx;
+	struct sysctl_oid_list *children;
+	char tn[32];
+	int unit;
+
+	ctx = device_get_sysctl_ctx(sc->sis_dev);
+	children = SYSCTL_CHILDREN(device_get_sysctl_tree(sc->sis_dev));
+
+	unit = device_get_unit(sc->sis_dev);
+	/*
+	 * Unlike most other controllers, NS DP83815/DP83816 controllers
+	 * seem to pad with 0xFF when it encounter short frames.  According
+	 * to RFC 1042 the pad bytes should be 0x00.  Turning this tunable
+	 * on will have driver pad manully but it's disabled by default
+	 * because it will consume extra CPU cycles for short frames.
+	 */
+	sc->sis_manual_pad = 0;
+	snprintf(tn, sizeof(tn), "dev.sis.%d.manual_pad", unit);
+	TUNABLE_INT_FETCH(tn, &sc->sis_manual_pad);
+	SYSCTL_ADD_INT(ctx, children, OID_AUTO, "manual_pad",
+	    CTLFLAG_RW, &sc->sis_manual_pad, 0, "Manually pad short frames");
+}
+
 static device_method_t sis_methods[] = {
 	/* Device interface */
 	DEVMETHOD(device_probe,		sis_probe),
diff --git a/sys/dev/sis/if_sisreg.h b/sys/dev/sis/if_sisreg.h
index 5bcdcae..42181a1 100644
--- a/sys/dev/sis/if_sisreg.h
+++ b/sys/dev/sis/if_sisreg.h
@@ -449,7 +449,10 @@ struct sis_softc {
 	device_t		sis_miibus;
 	uint8_t			sis_type;
 	uint8_t			sis_rev;
-	uint8_t			sis_link;
+	uint32_t		sis_flags;
+#define	SIS_FLAG_MANUAL_PAD	0x0800
+#define	SIS_FLAG_LINK		0x8000
+	int			sis_manual_pad;
 	uint32_t		sis_srr;
 	struct sis_desc		*sis_rx_list;
 	struct sis_desc		*sis_tx_list;