Hi,
I'm working on a project based around a SMARC format computer-on-a-module with a Rockchip RK3399 CPU. On the same motherboard we have a SJA1105 switch. The CPU runs Linux (5.4) and uses the NET_DSA_SJA1105 driver.
Our CPU needs to communicate with other devices over Ethernet so the CPU needs to be connected to the switch.
In the SJA1105 datasheet and in the Linux kernel device tree examples the host cpu is always connected to the switch as a fixed link directly over xMII. (https://www.kernel.org/doc/Documentation/devicetree/bindings/net/dsa/sja1105.txt)
We cannot do this as our SMARC module only gives us pin output from the RK3399 Ethernet integrated PHY, we do not have physical access directly to the xMII interface on the CPU no matter how much we would want to.
Also in the SJA1105 datasheet it says the following:
"Note that Ethernet connectivity to the host processor is only needed if the system has to support AVB operation or other bridge management protocols such as STP/RSTP. If such operations are not needed, all the ports can be used for data traffic."
Since we don't need AVB or STP/RSTP and since we anyway don't have access to the cpu xMII interface we have decided to just use the switch as a normal 5-port switch with PHY interfaces on every port. 4 ports where the PHY's actually goes to real RJ45 connectors and one port where the PHY is hardwired in the circuit board to the PHY that we get from our CPU on the SMARC board. This would give us a Linux device tree looking something like this:
(only SJA1105 relevant part shown, indentation also became screwed when pasted here)
&spi2 {
status = "okay";
#address-cells = <1>;
#size-cells = <0>;
num-cs = <2>;
cs-gpios = <&gpio2 RK_PB4 GPIO_ACTIVE_LOW>, <&gpio1 RK_PA3 GPIO_ACTIVE_LOW>;
sja1105_1: sja1105@1 {
status = "okay";
reg = <1>;
#address-cells = <1>;
#size-cells = <0>;
clocks = <ðswitch_osc>;
compatible = "nxp,sja1105t";
spi-max-frequency = <25000000>;
fsl,spi-cs-sck-delay = <1000>;
fsl,spi-sck-cs-delay = <1000>;
spi-cpha;
pinctrl-names = "default";
pinctrl-0 = <ðswitch_pins>;
reset-gpios = <&gpio4 RK_PC5 GPIO_ACTIVE_HIGH>;
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
/* Implicit "sja1105,role-mac;" */
label = "eth0";
phy-handle = <&rmii_phy0>;
phy-mode = "rmii";
reg = <0>;
};
port@1 {
/* Implicit "sja1105,role-mac;" */
label = "lan1";
phy-handle = <&rmii_phy1>;
phy-mode = "rmii";
reg = <1>;
};
port@2 {
/* Implicit "sja1105,role-mac;" */
label = "lan2";
phy-handle = <&rmii_phy2>;
phy-mode = "rmii";
reg = <2>;
};
port@3 {
/* Implicit "sja1105,role-mac;" */
phy-handle = <&rmii_phy3>;
label = "lan3";
phy-mode = "rmii";
reg = <3>;
};
port@4 {
/* Implicit "sja1105,role-mac;" */
phy-handle = <&rmii_phy4>;
label = "lan4";
phy-mode = "rmii";
reg = <4>;
};
};
};
};
This devicetree is valid and compiles, however during the probe the NET_DSA_SJA1105 fails because it cannot find a HOST CPU port (as we have not specified one). This error comes from net/dsa/dsa2.c *dsa_tree_find_first_cpu(struct dsa_switch_tree *dst) so it's not specific to sja1105 part of the driver but rather deeper in the Linux Distributed Switch Architecture.
In all devicetree examples there is always one port configured as host cpu connected with fixed link over xMII, for example like this:
port@4 {
/* Internal port connected to eth2 */
ethernet = <&enet2>;
phy-mode = "rgmii";
reg = <4>;
/* Implicit "sja1105,role-phy;" */
fixed-link {
speed = <1000>;
full-duplex;
};
};
If I try to modify my device tree to have the ports look something more like this:
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
/* Implicit "sja1105,role-phy;" */
ethernet = <&gmac>;
phy-mode = "rmii";
reg = <0>;
fixed-link {
speed = <100>;
full-duplex;
};
};
port@1 {
/* Implicit "sja1105,role-mac;" */
label = "lan1";
phy-handle = <&rmii_phy1>;
phy-mode = "rmii";
reg = <1>;
};
port@2 {
/* Implicit "sja1105,role-mac;" */
label = "lan2";
phy-handle = <&rmii_phy2>;
phy-mode = "rmii";
reg = <2>;
};
port@3 {
/* Implicit "sja1105,role-mac;" */
phy-handle = <&rmii_phy3>;
label = "lan3";
phy-mode = "rmii";
reg = <3>;
};
port@4 {
/* Implicit "sja1105,role-mac;" */
phy-handle = <&rmii_phy4>;
label = "lan4";
phy-mode = "rmii";
reg = <4>;
};
};
Then the driver is satisfied and probes successfully and sets up the SJA1105 switch. Ports 1-4 work
but port 0 (where CPU is connected via a PHY) does of course not work as it's now configured as xMII would be directly connected to it when in reality we have a PHY there in between the SJA1105 and the host CPU.
Is this a limitation the the DSA SJA1105 Linux driver, that you always must configure a fixed link over xMII? Can I somehow configure directly from the device tree that i DO NOT wish to have a dedicated cpu host port at all but rather just 5 normal ports (of which one then happens to so be connected to the CPU via a PHY...) Or can I configure the CPU host port to be there as a fixed-link, but explicitly specify that there is actually a PHY there also and not a xMII interface? I have tried dozens and dozens of combinations and still not found any way to configure this so that it will work with our supposedly very simple setup. Am I just missing something really obviously simple here? Any ideas how to proceed? Or is this just not possible with the Linux DSA SJA1105 driver?
Regards
