From e4700dbe992ecea72d4f07afbfa3ecd5dd21586f Mon Sep 17 00:00:00 2001
From: jmallett <jmallett@FreeBSD.org>
Date: Mon, 29 Nov 2010 21:04:00 +0000
Subject: [PATCH] Don't free the work queue entry that we're using to hold the
 scatter-gather list on exit from the transmit path.  The scatter-gather list
 itself can be asynchronously DMAed to the transmit hardware, and we could
 actually lock up the transmitter if any of a number of races around this were
 lost.

Instead, let the PKO free the scatter-gather list when it is done with it, and
use the "i" bit in each segment of the packet to avoid having them go into the
FPA.

This fixes an unrecoverable transmit stall under transmit load.

MFC after:	3 days
---
 sys/mips/cavium/octe/ethernet-tx.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/sys/mips/cavium/octe/ethernet-tx.c b/sys/mips/cavium/octe/ethernet-tx.c
index fc5145891304..887d771b2b36 100644
--- a/sys/mips/cavium/octe/ethernet-tx.c
+++ b/sys/mips/cavium/octe/ethernet-tx.c
@@ -143,6 +143,7 @@ int cvm_oct_xmit(struct mbuf *m, struct ifnet *ifp)
 		/* Build the PKO command */
 		pko_command.u64 = 0;
 		pko_command.s.segs = 1;
+		pko_command.s.dontfree = 1; /* Do not put this buffer into the FPA.  */
 
 		work = NULL;
 	} else {
@@ -164,6 +165,7 @@ int cvm_oct_xmit(struct mbuf *m, struct ifnet *ifp)
 
 			/* Build the PKO buffer pointer */
 			hw_buffer.u64 = 0;
+			hw_buffer.s.i = 1; /* Do not put this buffer into the FPA.  */
 			hw_buffer.s.addr = cvmx_ptr_to_phys(n->m_data);
 			hw_buffer.s.pool = 0;
 			hw_buffer.s.size = n->m_len;
@@ -182,12 +184,11 @@ int cvm_oct_xmit(struct mbuf *m, struct ifnet *ifp)
 		pko_command.u64 = 0;
 		pko_command.s.segs = segs;
 		pko_command.s.gather = 1;
+		pko_command.s.dontfree = 0; /* Put the WQE above back into the FPA.  */
 	}
 
 	/* Finish building the PKO command */
 	pko_command.s.n2 = 1; /* Don't pollute L2 with the outgoing packet */
-	pko_command.s.dontfree = 1;
-	pko_command.s.reg0 = priv->fau+qos*4;
 	pko_command.s.reg0 = priv->fau+qos*4;
 	pko_command.s.total_bytes = m->m_pkthdr.len;
 	pko_command.s.size0 = CVMX_FAU_OP_SIZE_32;
@@ -200,6 +201,11 @@ int cvm_oct_xmit(struct mbuf *m, struct ifnet *ifp)
 		pko_command.s.ipoffp1 = ETHER_HDR_LEN + 1;
 	}
 
+	/*
+	 * XXX
+	 * Could use a different free queue (and different FAU address) per
+	 * core instead of per QoS, to reduce contention here.
+	 */
 	IF_LOCK(&priv->tx_free_queue[qos]);
 	if (USE_ASYNC_IOBDMA) {
 		/* Get the number of mbufs in use by the hardware */
@@ -242,8 +248,6 @@ int cvm_oct_xmit(struct mbuf *m, struct ifnet *ifp)
 		/* Pass it to any BPF listeners.  */
 		ETHER_BPF_MTAP(ifp, m);
 	}
-	if (work != NULL)
-		cvmx_fpa_free(work, CVMX_FPA_WQE_POOL, DONT_WRITEBACK(1));
 
 	/* Free mbufs not in use by the hardware */
 	if (_IF_QLEN(&priv->tx_free_queue[qos]) > in_use) {