Fix the last serious bug I've been chasing:

The DP83820/83821 has an undocumented limitation concerning jumbo frames
and TX checksum offload. In order for TX checksum offload to work, the
outgoing frame must fit entirely within the TX FIFO, which is 8192 bytes
in size. This isn't a problem, until you try to send a 9000-byte frame,
at which point the TX DMA engine goes to sleep. It turns out that if
you want to send a jumbo frame larger than 8170 bytes (8192 - 64), you
have to turn off the TX checksum support.

As a workaround, I changed nge_ioctl() so that if the user selects an
MTU larger than 8152 bytes, we clear the if_hwassist flags. The flags
will be set again once the MTU is reduced to a smaller value.

1 files changed, 41 insertions, 23 deletions

diff --git a/sys/dev/nge/if_nge.c b/sys/dev/nge/if_nge.c
index ff1b53d..2dcee41 100644
--- a/sys/dev/nge/if_nge.c
+++ b/sys/dev/nge/if_nge.c
@@ -69,10 +69,22 @@
  * via software. This affects the size of certain fields in the DMA
  * descriptors.
  *
- * As far as I can tell, the 83820 and 83821 are decent chips, marred by
- * only one flaw: the RX buffers must be aligned on 64-bit boundaries.
- * So far this is the only gigE MAC that I've encountered with this
- * requirement.
+ * There are two bugs/misfeatures in the 83820/83821 that I have
+ * discovered so far:
+ *
+ * - Receive buffers must be aligned on 64-bit boundaries, which means
+ *   you must resort to copying data in order to fix up the payload
+ *   alignment.
+ *
+ * - In order to transmit jumbo frames larger than 8170 bytes, you have
+ *   to turn off transmit checksum offloading, because the chip can't
+ *   compute the checksum on an outgoing frame unless it fits entirely
+ *   within the TX FIFO, which is only 8192 bytes in size. If you have
+ *   TX checksum offload enabled and you transmit attempt to transmit a
+ *   frame larger than 8170 bytes, the transmitter will wedge.
+ *
+ * To work around the latter problem, TX checksum offload is disabled
+ * if the user selects an MTU larger than 8152 (8170 - 18).
  */
 
 #include "vlan.h"
@@ -1288,20 +1300,18 @@ static void nge_rxeof(sc)
 		m_adj(m, sizeof(struct ether_header));
 
 		/* Do IP checksum checking. */
-		if (ifp->if_hwassist) {
-			if (extsts & NGE_RXEXTSTS_IPPKT)
-				m->m_pkthdr.csum_flags |= CSUM_IP_CHECKED;
-			if (!(extsts & NGE_RXEXTSTS_IPCSUMERR))
-				m->m_pkthdr.csum_flags |= CSUM_IP_VALID;
-			if ((extsts & NGE_RXEXTSTS_TCPPKT &&
-			    !(extsts & NGE_RXEXTSTS_TCPCSUMERR)) ||
-			    (extsts & NGE_RXEXTSTS_UDPPKT &&
-			    !(extsts & NGE_RXEXTSTS_UDPCSUMERR))) {
-				m->m_pkthdr.csum_flags |=
-				    CSUM_DATA_VALID|CSUM_PSEUDO_HDR;
-				m->m_pkthdr.csum_data = 0xffff;
-			}
-                }
+		if (extsts & NGE_RXEXTSTS_IPPKT)
+			m->m_pkthdr.csum_flags |= CSUM_IP_CHECKED;
+		if (!(extsts & NGE_RXEXTSTS_IPCSUMERR))
+			m->m_pkthdr.csum_flags |= CSUM_IP_VALID;
+		if ((extsts & NGE_RXEXTSTS_TCPPKT &&
+		    !(extsts & NGE_RXEXTSTS_TCPCSUMERR)) ||
+		    (extsts & NGE_RXEXTSTS_UDPPKT &&
+		    !(extsts & NGE_RXEXTSTS_UDPCSUMERR))) {
+			m->m_pkthdr.csum_flags |=
+			    CSUM_DATA_VALID|CSUM_PSEUDO_HDR;
+			m->m_pkthdr.csum_data = 0xffff;
+		}
 
 #if NVLAN > 0
 		/*
@@ -1721,8 +1731,7 @@ static void nge_init(xsc)
 	 * Enable hardware checksum validation for all IPv4
 	 * packets, do not reject packets with bad checksums.
 	 */
-	if (ifp->if_hwassist)
-		CSR_WRITE_4(sc, NGE_VLAN_IP_RXCTL, NGE_VIPRXCTL_IPCSUM_ENB);
+	CSR_WRITE_4(sc, NGE_VLAN_IP_RXCTL, NGE_VIPRXCTL_IPCSUM_ENB);
 
 #if NVLAN > 0
 	/*
@@ -1740,8 +1749,7 @@ static void nge_init(xsc)
 	/*
 	 * Enable TX IPv4 checksumming on a per-packet basis.
 	 */
-	if (ifp->if_hwassist)
-		CSR_WRITE_4(sc, NGE_VLAN_IP_TXCTL, NGE_VIPTXCTL_CSUM_PER_PKT);
+	CSR_WRITE_4(sc, NGE_VLAN_IP_TXCTL, NGE_VIPTXCTL_CSUM_PER_PKT);
 
 #if NVLAN > 0
 	/*
@@ -1856,8 +1864,18 @@ static int nge_ioctl(ifp, command, data)
 	case SIOCSIFMTU:
 		if (ifr->ifr_mtu > NGE_JUMBO_MTU)
 			error = EINVAL;
-		else
+		else {
 			ifp->if_mtu = ifr->ifr_mtu;
+			/*
+			 * Workaround: if the MTU is larger than
+			 * 8152 (TX FIFO size minus 64 minus 18), turn off
+			 * TX checksum offloading.
+			 */
+			if (ifr->ifr_mtu == 8152)
+				ifp->if_hwassist = 0;
+			else
+				ifp->if_hwassist = NGE_CSUM_FEATURES;
+		}
 		break;
 	case SIOCSIFFLAGS:
 		if (ifp->if_flags & IFF_UP) {