macb: allow GEM to have configurable receive buffer size

GEM has configurable receive buffer sizes so requires this to be
programmed up.  Any size < 2048 and a multiple of 64 bytes is permitted.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
index 71424aa..1931078 100644
--- a/drivers/net/ethernet/cadence/macb.h
+++ b/drivers/net/ethernet/cadence/macb.h
@@ -64,6 +64,7 @@
 /* GEM register offsets. */
 #define GEM_NCFGR				0x0004
 #define GEM_USRIO				0x000c
+#define GEM_DMACFG				0x0010
 #define GEM_HRB					0x0080
 #define GEM_HRT					0x0084
 #define GEM_SA1B				0x0088
@@ -154,6 +155,10 @@
 #define GEM_DBW64				1
 #define GEM_DBW128				2
 
+/* Bitfields in DMACFG. */
+#define GEM_RXBS_OFFSET				16
+#define GEM_RXBS_SIZE				8
+
 /* Bitfields in NSR */
 #define MACB_NSR_LINK_OFFSET			0
 #define MACB_NSR_LINK_SIZE			1