Rework the transmit register handling. In em_encap() store index of

the EOP descriptor in the first descriptor of the packet. And then
in em_txeof() search for DD bits set only in the EOP descriptors,
embedding the cleanup of all packet's descriptors into inner loop.

This change is important for future chips, where DD bit is going
to be set only on the EOP descriptors.

Submitted by:	jfv

2 files changed, 79 insertions, 33 deletions

diff --git a/sys/dev/em/if_em.c b/sys/dev/em/if_em.c
index 0803ce7..803341e 100644
--- a/sys/dev/em/if_em.c
+++ b/sys/dev/em/if_em.c
@@ -1464,11 +1464,11 @@ em_encap(struct adapter *adapter, struct mbuf **m_headp)
 	struct ifnet		*ifp = adapter->ifp;
 	bus_dma_segment_t	segs[EM_MAX_SCATTER];
 	bus_dmamap_t		map;
-	struct em_buffer	*tx_buffer, *tx_buffer_last;
+	struct em_buffer	*tx_buffer, *tx_buffer_mapped;
 	struct em_tx_desc	*current_tx_desc;
 	struct mbuf		*m_head;
 	uint32_t		txd_upper, txd_lower, txd_used, txd_saved;
-	int			nsegs, i, j;
+	int			nsegs, i, j, first, last = 0;
 	int			error, do_tso, tso_desc = 0;
 
 	m_head = *m_headp;
@@ -1543,9 +1543,15 @@ em_encap(struct adapter *adapter, struct mbuf **m_headp)
 
 	/*
 	 * Map the packet for DMA.
+	 *
+	 * Capture the first descriptor index,
+	 * this descriptor will have the index
+	 * of the EOP which is the only one that
+	 * now gets a DONE bit writeback.
 	 */
-	tx_buffer = &adapter->tx_buffer_area[adapter->next_avail_tx_desc];
-	tx_buffer_last = tx_buffer;
+	first = adapter->next_avail_tx_desc;
+	tx_buffer = &adapter->tx_buffer_area[first];
+	tx_buffer_mapped = tx_buffer;
 	map = tx_buffer->map;
 
 	error = bus_dmamap_load_mbuf_sg(adapter->txtag, map, *m_headp, segs,
@@ -1658,10 +1664,12 @@ em_encap(struct adapter *adapter, struct mbuf **m_headp)
 					(adapter->txd_cmd | txd_lower |
 					(uint16_t)desc_array.descriptor[counter].length));
 				current_tx_desc->upper.data = htole32((txd_upper));
+				last = i;
 				if (++i == adapter->num_tx_desc)
 					i = 0;
 
 				tx_buffer->m_head = NULL;
+				tx_buffer->next_eop = -1;
 				txd_used++;
 			}
 		} else {
@@ -1693,6 +1701,7 @@ em_encap(struct adapter *adapter, struct mbuf **m_headp)
 				adapter->txd_cmd | txd_lower | 4);
 				current_tx_desc->upper.data =
 				    htole32(txd_upper);
+				last = i;
 				if (++i == adapter->num_tx_desc)
 					i = 0;
 			} else {
@@ -1701,10 +1710,12 @@ em_encap(struct adapter *adapter, struct mbuf **m_headp)
 				adapter->txd_cmd | txd_lower | seg_len);
 				current_tx_desc->upper.data =
 				    htole32(txd_upper);
+				last = i;
 				if (++i == adapter->num_tx_desc)
 					i = 0;
 			}
 			tx_buffer->m_head = NULL;
+			tx_buffer->next_eop = -1;
 		}
 	}
 
@@ -1727,14 +1738,23 @@ em_encap(struct adapter *adapter, struct mbuf **m_headp)
 	}
 
 	tx_buffer->m_head = m_head;
-	tx_buffer_last->map = tx_buffer->map;
+	tx_buffer_mapped->map = tx_buffer->map;
 	tx_buffer->map = map;
 	bus_dmamap_sync(adapter->txtag, map, BUS_DMASYNC_PREWRITE);
 
 	/*
-	 * Last Descriptor of Packet needs End Of Packet (EOP).
+	 * Last Descriptor of Packet
+	 * needs End Of Packet (EOP)
+	 * and Report Status (RS)
+	 */
+	current_tx_desc->lower.data |=
+	    htole32(E1000_TXD_CMD_EOP | E1000_TXD_CMD_RS);
+	/*
+	 * Keep track in the first buffer which
+	 * descriptor will be written back
 	 */
-	current_tx_desc->lower.data |= htole32(E1000_TXD_CMD_EOP);
+	tx_buffer = &adapter->tx_buffer_area[first];
+	tx_buffer->next_eop = last;
 
 	/*
 	 * Advance the Transmit Descriptor Tail (Tdt), this tells the E1000
@@ -2653,7 +2673,7 @@ em_setup_transmit_structures(struct adapter *adapter)
 	}
 
 	adapter->next_avail_tx_desc = 0;
-	adapter->oldest_used_tx_desc = 0;
+	adapter->next_tx_to_clean = 0;
 
 	/* Set number of descriptors available */
 	adapter->num_tx_desc_avail = adapter->num_tx_desc;
@@ -2739,8 +2759,8 @@ em_initialize_transmit_unit(struct adapter *adapter)
 	/* This write will effectively turn on the transmit unit. */
 	E1000_WRITE_REG(&adapter->hw, TCTL, reg_tctl);
 
-	/* Setup Transmit Descriptor Settings for this adapter */
-	adapter->txd_cmd = E1000_TXD_CMD_IFCS | E1000_TXD_CMD_RS;
+	/* Setup Transmit Descriptor Base Settings */
+	adapter->txd_cmd = E1000_TXD_CMD_IFCS;
 
 	if (adapter->tx_int_delay.value > 0)
 		adapter->txd_cmd |= E1000_TXD_CMD_IDE;
@@ -2923,6 +2943,7 @@ em_transmit_checksum_setup(struct adapter *adapter, struct mbuf *mp,
 	TXD->cmd_and_length =
 	    htole32(adapter->txd_cmd | E1000_TXD_CMD_DEXT | cmd);
 	tx_buffer->m_head = NULL;
+	tx_buffer->next_eop = -1;
 
 	if (++curr_txd == adapter->num_tx_desc)
 		curr_txd = 0;
@@ -3099,9 +3120,9 @@ em_tso_setup(struct adapter *adapter, struct mbuf *mp, uint32_t *txd_upper,
 static void
 em_txeof(struct adapter *adapter)
 {
-	int i, num_avail;
+	int first, last, done, num_avail;
 	struct em_buffer *tx_buffer;
-	struct em_tx_desc   *tx_desc;
+	struct em_tx_desc   *tx_desc, *eop_desc;
 	struct ifnet   *ifp = adapter->ifp;
 
 	EM_LOCK_ASSERT(adapter);
@@ -3110,38 +3131,62 @@ em_txeof(struct adapter *adapter)
 		return;
 
 	num_avail = adapter->num_tx_desc_avail;
-	i = adapter->oldest_used_tx_desc;
+	first = adapter->next_tx_to_clean;
+	tx_desc = &adapter->tx_desc_base[first];
+	tx_buffer = &adapter->tx_buffer_area[first];
+	last = tx_buffer->next_eop;
+	eop_desc = &adapter->tx_desc_base[last];
 
-	tx_buffer = &adapter->tx_buffer_area[i];
-	tx_desc = &adapter->tx_desc_base[i];
+	/*
+	 * Now calculate the terminating index
+	 * for the cleanup loop below.
+	 */
+	if (++last == adapter->num_tx_desc)
+		last = 0;
+	done = last;
 
 	bus_dmamap_sync(adapter->txdma.dma_tag, adapter->txdma.dma_map,
 	    BUS_DMASYNC_POSTREAD);
-	while (tx_desc->upper.fields.status & E1000_TXD_STAT_DD) {
+	while (eop_desc->upper.fields.status & E1000_TXD_STAT_DD) {
+		/* We clean the range of the packet */
+		while (first != done) {
+			tx_desc->upper.data = 0;
+			tx_desc->lower.data = 0;
+			num_avail++;
+
+			if (tx_buffer->m_head) {
+				ifp->if_opackets++;
+				bus_dmamap_sync(adapter->txtag, tx_buffer->map,
+				    BUS_DMASYNC_POSTWRITE);
+				bus_dmamap_unload(adapter->txtag,
+				    tx_buffer->map);
 
-		tx_desc->upper.data = 0;
-		num_avail++;
+				m_freem(tx_buffer->m_head);
+				tx_buffer->m_head = NULL;
+			}
+			tx_buffer->next_eop = -1;
 
-		if (tx_buffer->m_head) {
-			ifp->if_opackets++;
-			bus_dmamap_sync(adapter->txtag, tx_buffer->map,
-			    BUS_DMASYNC_POSTWRITE);
-			bus_dmamap_unload(adapter->txtag, tx_buffer->map);
+			if (++first == adapter->num_tx_desc)
+				first = 0;
 
-			m_freem(tx_buffer->m_head);
-			tx_buffer->m_head = NULL;
+			tx_buffer = &adapter->tx_buffer_area[first];
+			tx_desc = &adapter->tx_desc_base[first];
 		}
-
-		if (++i == adapter->num_tx_desc)
-			i = 0;
-
-		tx_buffer = &adapter->tx_buffer_area[i];
-		tx_desc = &adapter->tx_desc_base[i];
+		/* See if we can continue to the next packet */
+		last = tx_buffer->next_eop;
+		if (last != -1) {
+			eop_desc = &adapter->tx_desc_base[last];
+			/* Get new done point */
+			if (++last == adapter->num_tx_desc)
+				last = 0;
+			done = last;
+		} else
+			break;
 	}
 	bus_dmamap_sync(adapter->txdma.dma_tag, adapter->txdma.dma_map,
 	    BUS_DMASYNC_PREREAD | BUS_DMASYNC_PREWRITE);
 
-	adapter->oldest_used_tx_desc = i;
+	adapter->next_tx_to_clean = first;
 
 	/*
 	 * If we have enough room, clear IFF_DRV_OACTIVE to tell the stack
diff --git a/sys/dev/em/if_em.h b/sys/dev/em/if_em.h
index 27f664e..33752c0 100644
--- a/sys/dev/em/if_em.h
+++ b/sys/dev/em/if_em.h
@@ -319,7 +319,7 @@ struct adapter {
 	struct em_dma_alloc	txdma;		/* bus_dma glue for tx desc */
 	struct em_tx_desc	*tx_desc_base;
 	uint32_t		next_avail_tx_desc;
-	uint32_t		oldest_used_tx_desc;
+	uint32_t		next_tx_to_clean;
 	volatile uint16_t	num_tx_desc_avail;
         uint16_t		num_tx_desc;
         uint32_t		txd_cmd;
@@ -398,6 +398,7 @@ typedef struct _em_vendor_info_t {
 
 
 struct em_buffer {
+	int		next_eop;	/* Index of the desc to watch */
         struct mbuf    *m_head;
         bus_dmamap_t    map;         /* bus_dma map for packet */
 };