tg3: Fix 5906 transmit hangs

The 5906 has trouble with fragments that are less than 8 bytes in size.
This patch works around the problem by pivoting the 5906's transmit
routine to tg3_start_xmit_dma_bug() and introducing a new SHORT_DMA_BUG
flag that enables code to detect and react to the problematic condition.
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tg3.c

@@ -5393,7 +5393,7 @@ static netdev_tx_t tg3_start_xmit_dma_bug(struct sk_buff *skb,
 	mss = 0;
 	if ((mss = skb_shinfo(skb)->gso_size) != 0) {
 		struct iphdr *iph;
-		int tcp_opt_len, ip_tcp_len, hdr_len;
+		u32 tcp_opt_len, ip_tcp_len, hdr_len;
 
 		if (skb_header_cloned(skb) &&
 		    pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) {
@@ -5424,8 +5424,10 @@ static netdev_tx_t tg3_start_xmit_dma_bug(struct sk_buff *skb,
 								 IPPROTO_TCP,
 								 0);
 
-		if ((tp->tg3_flags2 & TG3_FLG2_HW_TSO) ||
-		    (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5705)) {
+		if (tp->tg3_flags2 & TG3_FLG2_HW_TSO_2)
+			mss |= hdr_len << 9;
+		else if ((tp->tg3_flags2 & TG3_FLG2_HW_TSO_1) ||
+			 GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5705) {
 			if (tcp_opt_len || iph->ihl > 5) {
 				int tsflags;
 
@@ -5460,6 +5462,9 @@ static netdev_tx_t tg3_start_xmit_dma_bug(struct sk_buff *skb,
 
 	would_hit_hwbug = 0;
 
+	if ((tp->tg3_flags3 & TG3_FLG3_SHORT_DMA_BUG) && len <= 8)
+		would_hit_hwbug = 1;
+
 	if ((tp->tg3_flags3 & TG3_FLG3_4G_DMA_BNDRY_BUG) &&
 	    tg3_4g_overflow_test(mapping, len))
 		would_hit_hwbug = 1;
@@ -5489,6 +5494,10 @@ static netdev_tx_t tg3_start_xmit_dma_bug(struct sk_buff *skb,
 
 			tnapi->tx_buffers[entry].skb = NULL;
 
+			if ((tp->tg3_flags3 & TG3_FLG3_SHORT_DMA_BUG) &&
+			    len <= 8)
+				would_hit_hwbug = 1;
+
 			if ((tp->tg3_flags3 & TG3_FLG3_4G_DMA_BNDRY_BUG) &&
 			    tg3_4g_overflow_test(mapping, len))
 				would_hit_hwbug = 1;
@@ -12625,9 +12634,13 @@ static int __devinit tg3_get_invariants(struct tg3 *tp)
 	}
 
 	if (!(tp->tg3_flags3 & TG3_FLG3_5755_PLUS)) {
+		if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5906)
+			tp->tg3_flags3 |= TG3_FLG3_SHORT_DMA_BUG;
+		else {
 			tp->tg3_flags3 |= TG3_FLG3_4G_DMA_BNDRY_BUG;
 			tp->tg3_flags3 |= TG3_FLG3_40BIT_DMA_LIMIT_BUG;
 		}
+	}
 
 	if (!(tp->tg3_flags2 & TG3_FLG2_5705_PLUS) ||
 	     (tp->tg3_flags2 & TG3_FLG2_5780_CLASS) ||
@@ -13987,8 +14000,7 @@ static int __devinit tg3_init_one(struct pci_dev *pdev,
 		goto err_out_iounmap;
 	}
 
-	if ((tp->tg3_flags3 & TG3_FLG3_5755_PLUS) ||
-	    GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5906)
+	if (tp->tg3_flags3 & TG3_FLG3_5755_PLUS)
 		dev->netdev_ops = &tg3_netdev_ops;
 	else
 		dev->netdev_ops = &tg3_netdev_ops_dma_bug;

drivers/net/tg3.h

@@ -2761,6 +2761,7 @@ struct tg3 {
 #define TG3_FLG3_ENABLE_RSS		0x00020000
 #define TG3_FLG3_4G_DMA_BNDRY_BUG	0x00080000
 #define TG3_FLG3_40BIT_DMA_LIMIT_BUG	0x00100000
+#define TG3_FLG3_SHORT_DMA_BUG		0x00200000
 
 	struct timer_list		timer;
 	u16				timer_counter;