Try to improve sky2 reliability a little bit.
At least one oops has been seen when setting the link down with
"ip li set eth0 down". The oops showed a NULL re->skb in sky2_receive().
Also backport some adjustments from 1.10.

--- ./drivers/net/sky2.c.orig	2007-02-16 14:32:04 +0100
+++ ./drivers/net/sky2.c	2007-02-17 18:35:12 +0100
@@ -58,9 +58,9 @@
  * a receive requires one (or two if using 64 bit dma).
  */
 
-#define RX_LE_SIZE	    	512
+#define RX_LE_SIZE	    	1024
 #define RX_LE_BYTES		(RX_LE_SIZE*sizeof(struct sky2_rx_le))
-#define RX_MAX_PENDING		(RX_LE_SIZE/2 - 2)
+#define RX_MAX_PENDING		(RX_LE_SIZE/6 - 2)
 #define RX_DEF_PENDING		RX_MAX_PENDING
 #define RX_SKB_ALIGN		8
 #define RX_BUF_WRITE		16
@@ -88,7 +88,7 @@
 module_param(debug, int, 0);
 MODULE_PARM_DESC(debug, "Debug level (0=none,...,16=all)");
 
-static int copybreak = 256;
+static int copybreak = 128;
 module_param(copybreak, int, 0);
 MODULE_PARM_DESC(copybreak, "Receive copy threshold");
 
@@ -451,6 +451,7 @@
 	}
 
 	gma_write16(hw, port, GM_GP_CTRL, reg);
+	gma_read16(hw, port, GM_GP_CTRL);
 
 	if (hw->chip_id != CHIP_ID_YUKON_FE)
 		gm_phy_write(hw, port, PHY_MARV_1000T_CTRL, ct1000);
@@ -1086,6 +1087,7 @@
 	if (err)
 		goto err_out;
 
+just_ints:
 	/* Enable interrupts from phy/mac for port */
 	imask = sky2_read32(hw, B0_IMSK);
 	imask |= portirq_msk[port];
@@ -1316,6 +1318,13 @@
 		struct tx_ring_info *re = sky2->tx_ring + put;
 		struct sk_buff *skb = re->skb;
 
+		// FIXME: it seems possible that sky2_rx_clean() flushes the ring below us.
+		if (!skb) {
+			printk(KERN_WARNING "sky2: %s: NULL skb in %s\n",
+			       dev->name, __FUNCTION__);
+			continue;
+		}
+
 		nxt = re->idx;
 		BUG_ON(nxt >= TX_RING_SIZE);
 		prefetch(sky2->tx_ring + nxt);
@@ -1388,6 +1397,7 @@
 	ctrl = gma_read16(hw, port, GM_GP_CTRL);
 	ctrl &= ~(GM_GPCR_TX_ENA | GM_GPCR_RX_ENA);
 	gma_write16(hw, port, GM_GP_CTRL, ctrl);
+	gma_read16(hw, port, GM_GP_CTRL);
 
 	sky2_write8(hw, SK_REG(port, GPHY_CTRL), GPC_RST_SET);
 
@@ -1477,6 +1487,7 @@
 	reg = gma_read16(hw, port, GM_GP_CTRL);
 	reg |= GM_GPCR_RX_ENA | GM_GPCR_TX_ENA;
 	gma_write16(hw, port, GM_GP_CTRL, reg);
+	gma_read16(hw, port, GM_GP_CTRL);
 
 	gm_phy_write(hw, port, PHY_MARV_INT_MASK, PHY_M_DEF_MSK);
 
@@ -1529,6 +1540,7 @@
 	reg = gma_read16(hw, port, GM_GP_CTRL);
 	reg &= ~(GM_GPCR_RX_ENA | GM_GPCR_TX_ENA);
 	gma_write16(hw, port, GM_GP_CTRL, reg);
+	gma_read16(hw, port, GM_GP_CTRL);
 
 	if (sky2->flow_status == FC_RX) {
 		/* restore Asymmetric Pause bit */
@@ -1720,6 +1732,7 @@
 
 	ctl = gma_read16(hw, sky2->port, GM_GP_CTRL);
 	gma_write16(hw, sky2->port, GM_GP_CTRL, ctl & ~GM_GPCR_RX_ENA);
+	gma_read16(hw, sky2->port, GM_GP_CTRL);
 	sky2_rx_stop(sky2);
 	sky2_rx_clean(sky2);
 
@@ -1742,6 +1755,7 @@
 		dev_close(dev);
 	else {
 		gma_write16(hw, sky2->port, GM_GP_CTRL, ctl);
+		gma_read16(hw, sky2->port, GM_GP_CTRL);
 
 		netif_wake_queue(dev);
 	}
@@ -1760,6 +1774,12 @@
 	struct ring_info *re = sky2->rx_ring + sky2->rx_next;
 	struct sk_buff *skb = NULL;
 
+	// FIXME: it seems possible that sky2_rx_clean() flushes the ring below us.
+	if (!re->skb) {
+		printk(KERN_WARNING "sky2: NULL skb in %s\n", __FUNCTION__);
+		return NULL;
+	}
+
 	if (unlikely(netif_msg_rx_status(sky2)))
 		printk(KERN_DEBUG PFX "%s: rx slot %u status 0x%x len %d\n",
 		       sky2->netdev->name, sky2->rx_next, status, length);