net: mv643xx_eth: proper initialization for Kirkwood SoCs

Ethernet controllers found on Kirkwood SoCs not only suffer from loosing
MAC address register contents on clock gating but also some important
registers are reset to values that would break ethernet. This patch
clears the CLK125_BYPASS_EN bit for DT enabled Kirkwood only by using
of_device_is_compatible() instead of #ifdefs. Non-DT Kirkwood is not
affected as it installs a clock gating workaround because of the MAC
address issue above. Other Orion SoCs do not suffer from register reset,
do not have the bit in question, or do not have the register at all.
Moreover, system controllers on PPC using this driver should also be
protected from clearing that bit.

Signed-off-by: Sebastian Hesselbarth <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/marvell/mv643xx_eth.c

···
 #define  LINK_UP			0x00000002
 #define TXQ_COMMAND			0x0048
 #define TXQ_FIX_PRIO_CONF		0x004c
+#define PORT_SERIAL_CONTROL1		0x004c
+#define  CLK125_BYPASS_EN		0x00000010
 #define TX_BW_RATE			0x0050
 #define TX_BW_MTU			0x0058
 #define TX_BW_BURST			0x005c
···
 	mp->port_num = pd->port_number;
 
 	mp->dev = dev;
+
+	/* Kirkwood resets some registers on gated clocks. Especially
+	 * CLK125_BYPASS_EN must be cleared but is not available on
+	 * all other SoCs/System Controllers using this driver.
+	 */
+	if (of_device_is_compatible(pdev->dev.of_node,
+				    "marvell,kirkwood-eth-port"))
+		wrlp(mp, PORT_SERIAL_CONTROL1,
+		     rdlp(mp, PORT_SERIAL_CONTROL1) & ~CLK125_BYPASS_EN);
 
 	/*
 	 * Start with a default rate, and if there is a clock, allow