dt-binding: net: sfp binding documentation

Add device-tree binding documentation SFP transceivers. Support for SFP
transceivers has been recently introduced (drivers/net/phy/sfp.c).
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/sff,sfp.txt

+Small Form Factor (SFF) Committee Small Form-factor Pluggable (SFP)
+Transceiver
+
+Required properties:
+
+- compatible : must be "sff,sfp"
+
+Optional Properties:
+
+- i2c-bus : phandle of an I2C bus controller for the SFP two wire serial
+  interface
+
+- mod-def0-gpios : GPIO phandle and a specifier of the MOD-DEF0 (AKA Mod_ABS)
+  module presence input gpio signal, active (module absent) high
+
+- los-gpios : GPIO phandle and a specifier of the Receiver Loss of Signal
+  Indication input gpio signal, active (signal lost) high
+
+- tx-fault-gpios : GPIO phandle and a specifier of the Module Transmitter
+  Fault input gpio signal, active (fault condition) high
+
+- tx-disable-gpios : GPIO phandle and a specifier of the Transmitter Disable
+  output gpio signal, active (Tx disable) high
+
+- rate-select0-gpios : GPIO phandle and a specifier of the Rx Signaling Rate
+  Select (AKA RS0) output gpio signal, low: low Rx rate, high: high Rx rate
+
+- rate-select1-gpios : GPIO phandle and a specifier of the Tx Signaling Rate
+  Select (AKA RS1) output gpio signal (SFP+ only), low: low Tx rate, high:
+  high Tx rate
+
+Example #1: Direct serdes to SFP connection
+
+sfp_eth3: sfp-eth3 {
+	compatible = "sff,sfp";
+	i2c-bus = <&sfp_1g_i2c>;
+	los-gpios = <&cpm_gpio2 22 GPIO_ACTIVE_HIGH>;
+	mod-def0-gpios = <&cpm_gpio2 21 GPIO_ACTIVE_LOW>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&cpm_sfp_1g_pins &cps_sfp_1g_pins>;
+	tx-disable-gpios = <&cps_gpio1 24 GPIO_ACTIVE_HIGH>;
+	tx-fault-gpios = <&cpm_gpio2 19 GPIO_ACTIVE_HIGH>;
+};
+
+&cps_emac3 {
+	phy-names = "comphy";
+	phys = <&cps_comphy5 0>;
+	sfp = <&sfp_eth3>;
+};
+
+Example #2: Serdes to PHY to SFP connection
+
+sfp_eth0: sfp-eth0 {
+	compatible = "sff,sfp";
+	i2c-bus = <&sfpp0_i2c>;
+	los-gpios = <&cps_gpio1 28 GPIO_ACTIVE_HIGH>;
+	mod-def0-gpios = <&cps_gpio1 27 GPIO_ACTIVE_LOW>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&cps_sfpp0_pins>;
+	tx-disable-gpios = <&cps_gpio1 29 GPIO_ACTIVE_HIGH>;
+	tx-fault-gpios  = <&cps_gpio1 26 GPIO_ACTIVE_HIGH>;
+};
+
+p0_phy: ethernet-phy@0 {
+	compatible = "ethernet-phy-ieee802.3-c45";
+	pinctrl-names = "default";
+	pinctrl-0 = <&cpm_phy0_pins &cps_phy0_pins>;
+	reg = <0>;
+	interrupt = <&cpm_gpio2 18 IRQ_TYPE_EDGE_FALLING>;
+	sfp = <&sfp_eth0>;
+};
+
+&cpm_eth0 {
+	phy = <&p0_phy>;
+	phy-mode = "10gbase-kr";
+};