net: macb: Add on the fly CPU endianness detection

Program management descriptor's access mode according to the
dynamically detected CPU endianness.
Signed-off-by: Arun Chandran <achandran@mvista.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb.c

@@ -1578,6 +1578,7 @@ static u32 macb_dbw(struct macb *bp)
 static void macb_configure_dma(struct macb *bp)
 {
 	u32 dmacfg;
+	u32 tmp, ncr;
 
 	if (macb_is_gem(bp)) {
 		dmacfg = gem_readl(bp, DMACFG) & ~GEM_BF(RXBS, -1L);
@@ -1586,10 +1587,23 @@ static void macb_configure_dma(struct macb *bp)
 			dmacfg = GEM_BFINS(FBLDO, bp->dma_burst_length, dmacfg);
 		dmacfg |= GEM_BIT(TXPBMS) | GEM_BF(RXBMS, -1L);
 		dmacfg &= ~GEM_BIT(ENDIA_PKT);
-		/* Tell the chip to byteswap descriptors on big-endian hosts */
-#ifdef __BIG_ENDIAN
-		dmacfg |= GEM_BIT(ENDIA_DESC);
-#endif
+
+		/* Find the CPU endianness by using the loopback bit of net_ctrl
+		 * register. save it first. When the CPU is in big endian we
+		 * need to program swaped mode for management descriptor access.
+		 */
+		ncr = macb_readl(bp, NCR);
+		__raw_writel(MACB_BIT(LLB), bp->regs + MACB_NCR);
+		tmp =  __raw_readl(bp->regs + MACB_NCR);
+
+		if (tmp == MACB_BIT(LLB))
+			dmacfg &= ~GEM_BIT(ENDIA_DESC);
+		else
+			dmacfg |= GEM_BIT(ENDIA_DESC); /* CPU in big endian */
+
+		/* Restore net_ctrl */
+		macb_writel(bp, NCR, ncr);
+
 		if (bp->dev->features & NETIF_F_HW_CSUM)
 			dmacfg |= GEM_BIT(TXCOEN);
 		else