net: phy: Add minimal support for QSGMII PHY

Based on Linux's support by Thomas Petazzoni:

    commit b9d12085f2f531fdea67f0361564e0812696227c
    Author: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
    Date:   Tue Apr 15 15:50:19 2014 +0200
    net: phy: add minimal support for QSGMII PHY

    This commit adds the necessary definitions for the PHY layer to
    recognize "qsgmii" as a valid PHY interface. A QSMII interface, as
    defined at
    http://en.wikipedia.org/wiki/Media_Independent_Interface#Quad_Serial_Gigabit_Media_Independent_Interface,
    is "is a method of combining four SGMII lines into a 5Gbit/s
    interface. QSGMII, like SGMII, uses LVDS signalling for the TX and RX
    data and a single LVDS clock signal. QSGMII uses significantly fewer
    signal lines than four SGMII busses."

    This type of MAC <-> PHY connection might require special handling on
    the MAC driver side, so it should be possible to express this type of
    MAC <-> PHY connection, for example in the Device Tree.

    Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
    Cc: devicetree@vger.kernel.org
    Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

drivers/of/of_net.c

@@ -28,6 +28,7 @@ static const char *phy_modes[] = {
 	[PHY_INTERFACE_MODE_RGMII_TXID] = "rgmii-txid",
 	[PHY_INTERFACE_MODE_RTBI]	= "rtbi",
 	[PHY_INTERFACE_MODE_SMII]	= "smii",
+	[PHY_INTERFACE_MODE_QSGMII]	= "qsgmii",
 };
 
 /**

include/linux/phy.h

@@ -54,6 +54,7 @@ typedef enum {
 	PHY_INTERFACE_MODE_RGMII_TXID,
 	PHY_INTERFACE_MODE_RTBI,
 	PHY_INTERFACE_MODE_SMII,
+	PHY_INTERFACE_MODE_QSGMII,
 } phy_interface_t;
 
 #define PHY_INIT_TIMEOUT	100000