smsx95xx: Add option to disable the crimes against truesize fix

It may improve iperf numbers on Pi 1, but may generate dmesg warnings and possibly cause network issues
See issue 1248.

Author: popcornmix

drivers/net/usb/smsc95xx.c

@@ -75,6 +75,10 @@ static bool turbo_mode = false;
 module_param(turbo_mode, bool, 0644);
 MODULE_PARM_DESC(turbo_mode, "Enable multiple frames per Rx transaction");
 
+static bool truesize_mode = false;
+module_param(truesize_mode, bool, 0644);
+MODULE_PARM_DESC(truesize_mode, "Report larger truesize value");
+
 static char *macaddr = ":";
 module_param(macaddr, charp, 0);
 MODULE_PARM_DESC(macaddr, "MAC address");
@@ -1841,6 +1845,8 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 				if (dev->net->features & NETIF_F_RXCSUM)
 					smsc95xx_rx_csum_offload(skb);
 				skb_trim(skb, skb->len - 4); /* remove fcs */
+				if (truesize_mode)
+					skb->truesize = size + sizeof(struct sk_buff);
 
 				return 1;
 			}
@@ -1858,6 +1864,8 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			if (dev->net->features & NETIF_F_RXCSUM)
 				smsc95xx_rx_csum_offload(ax_skb);
 			skb_trim(ax_skb, ax_skb->len - 4); /* remove fcs */
+			if (truesize_mode)
+				ax_skb->truesize = size + sizeof(struct sk_buff);
 
 			usbnet_skb_return(dev, ax_skb);
 		}