r8169: quirk for the 8110sb on arm platform

Inverting the write ordering of the TxDescAddr{High/Low} registers
suffices to trigger a sabbat of PCI errors which make the device
completely dysfunctional. The issue has not been reported on a
different platform.

Switching from MMIO accesses to I/O ones as done in Realtek's
own driver fixes (papers over ?) the bug as well but I am not
thrilled to see everyone pay the I/O price for an obscure bug.

This is the minimal change to handle the issue.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Reported-by: Lennert Buytenhek <buytenh@wantstofly.org>

drivers/net/r8169.c

@@ -1904,10 +1904,15 @@ rtl8169_hw_start(struct net_device *dev)
 	 */
 	RTL_W16(IntrMitigate, 0x0000);
 
-	RTL_W32(TxDescStartAddrLow, ((u64) tp->TxPhyAddr & DMA_32BIT_MASK));
+	/*
+	 * Magic spell: some iop3xx ARM board needs the TxDescAddrHigh
+	 * register to be written before TxDescAddrLow to work.
+	 * Switching from MMIO to I/O access fixes the issue as well.
+	 */
 	RTL_W32(TxDescStartAddrHigh, ((u64) tp->TxPhyAddr >> 32));
-	RTL_W32(RxDescAddrLow, ((u64) tp->RxPhyAddr & DMA_32BIT_MASK));
+	RTL_W32(TxDescStartAddrLow, ((u64) tp->TxPhyAddr & DMA_32BIT_MASK));
 	RTL_W32(RxDescAddrHigh, ((u64) tp->RxPhyAddr >> 32));
+	RTL_W32(RxDescAddrLow, ((u64) tp->RxPhyAddr & DMA_32BIT_MASK));
 	RTL_W8(ChipCmd, CmdTxEnb | CmdRxEnb);
 	RTL_W8(Cfg9346, Cfg9346_Lock);