[PATCH] ixgb: Limit number of Rx Descriptors to 512

Workaround for a Si Erratum. When more that 512 Rx descriptors are used,
there may be Rx data corruption.
Signed-off-by: Ganesh Venkatesan <ganesh.venkatesan@intel.com>

drivers/net/ixgb/ixgb.h

@@ -85,6 +85,16 @@ struct ixgb_adapter;
 
 #define IXGB_ERR(args...) printk(KERN_ERR "ixgb: " args)
 
+
+/* hardware cannot reliably support more than 512 descriptors owned by
+ * hardware descrioptor cache otherwise an unreliable ring under heavy 
+ * recieve load may result */
+/* #define DEFAULT_RXD	   1024 */
+/* #define MAX_RXD	   4096 */
+#define DEFAULT_RXD	512
+#define MAX_RXD	512
+#define MIN_RXD	 64
+
 /* Supported Rx Buffer Sizes */
 #define IXGB_RXBUFFER_2048  2048
 #define IXGB_RXBUFFER_4096  4096

drivers/net/ixgb/ixgb_param.c

@@ -177,9 +177,6 @@ IXGB_PARAM(IntDelayEnable, "Transmit Interrupt Delay Enable");
 #define MAX_TXD				   4096
 #define MIN_TXD				     64
 
-#define DEFAULT_RXD			   1024
-#define MAX_RXD				   4096
-#define MIN_RXD				     64
 
 #define DEFAULT_TIDV	   		     32
 #define MAX_TIDV			 0xFFFF