Device Tree for PHY-less connection to a DSA switch - linux

Question

We have a little problem with creating a device tree for our configuration of a Marvell DSA switch and a Xilinx Zynq processor. They are connected like this:
|——————————————| |——————————————————————————————|
| e000b000—|———— SGMII ————|—port6 (0x16) port3 —— PHY3
| Zynq | | mv88e6321 |
| e000c000—|—x x—|—port5 port4 —— PHY4
|——————————————| |——————————————————————————————|
|___________ MDIO _______________|
And we have a device tree for the Linux kernel, which looks like this:
ps7_ethernet_0: ps7-ethernet#e000b000 {
#address-cells = <1>;
#size-cells = <0>;
clock-names = "ref_clk", "aper_clk";
clocks = <&clkc 13>, <&clkc 30>;
compatible = "xlnx,ps7-ethernet-1.00.a";
interrupt-parent = <&ps7_scugic_0>;
interrupts = <0 22 4>;
local-mac-address = [00 0a 35 00 00 00];
phy-handle = <&phy0>;
phy-mode = "gmii";
reg = <0xe000b000 0x1000>;
xlnx,ptp-enet-clock = <0x69f6bcb>;
xlnx,enet-reset = "";
xlnx,eth-mode = <0x0>;
xlnx,has-mdio = <0x1>;
mdio_0: mdio {
#address-cells = <1>;
#size-cells = <0>;
phy0: phy#16 {
compatiable = "marvell,dsa";
reg = <0x16>;
} ;
} ;
} ;
dsa#0 {
compatible = "marvell,dsa";
#address-cells = <2>;
#size-cells = <0>;
interrupts = <10>;
dsa,ethernet = <&ps7_ethernet_0>;
dsa,mii-bus = <&mdio_0>;
switch#0 {
#address-cells = <1>;
#size-cells = <0>;
reg = <0 0>;
port#3 {
reg = <3>;
label = "lan0";
};
port#4 {
reg = <4>;
label = "lan1";
};
port#5 {
reg = <5>;
label = "lan2";
};
port#6 {
reg = <6>;
label = "cpu";
};
};
};
} ;
The problem is, as you can see from the picture, there is no PHY attached to the port 6, i.e. the connection between the Zynq and the switch is PHY-less, but I had to specify <phy0> in the device tree to make the dsa driver to see the switch. But then it tries to talk to a non-existent PHY and fails, obviously.
So the question is: how to create a proper device tree for a dsa switch connected to a processor like this?
Thank you for any help!
(There is a somewhat similar question P1010 MAC to Switch port direct connection without PHY but I cannot comment on it and there is no answer, unfortunately)

Answer 1

Instead of specifying &phy0 when there is none, you can write it as fixed-link
fixed-link = <0 1 1000 0 0>;
Where 0 is emulated PHY ID, 1-> full-duplex and speed is 1000 Mb/s.
You would also want to disable autonegotiation for the processor port to which switch port 6 is connected.
ps7_ethernet_0: ps7-ethernet#e000b000 {
#address-cells = <1>;
#size-cells = <0>;
clock-names = "ref_clk", "aper_clk";
clocks = <&clkc 13>, <&clkc 30>;
compatible = "xlnx,ps7-ethernet-1.00.a";
interrupt-parent = <&ps7_scugic_0>;
interrupts = <0 22 4>;
local-mac-address = [00 0a 35 00 00 00];
fixed-link = <0 1 1000 0 0>;
phy-mode = "gmii";
reg = <0xe000b000 0x1000>;
xlnx,ptp-enet-clock = <0x69f6bcb>;
xlnx,enet-reset = "";
xlnx,eth-mode = <0x0>;
xlnx,has-mdio = <0x1>;
mdio_0: mdio {
#address-cells = <1>;
#size-cells = <0>;
} ;
} ;
dsa#0 {
compatible = "marvell,dsa";
#address-cells = <2>;
#size-cells = <0>;
interrupts = <10>;
dsa,ethernet = <&ps7_ethernet_0>;
dsa,mii-bus = <&mdio_0>;
switch#0 {
#address-cells = <1>;
#size-cells = <0>;
reg = <22 0>;
port#3 {
reg = <3>;
label = "lan0";
};
port#4 {
reg = <4>;
label = "lan1";
};
port#5 {
reg = <5>;
label = "lan2";
};
port#6 {
reg = <6>;
label = "cpu";
};
};
};
} ;
I'm assuming switch chip SMI address is 0x16; if not make reg = <22,0> to <0,0> as before under switch#0.
Also you may need to add mdio driver reg address and compatible property , which are not specified in your device tree.