On Thu, Aug 19, 2021 at 04:52:43PM -0700, Saravana Kannan wrote:

On Thu, Aug 19, 2021 at 6:35 AM Andrew Lunn [off-list ref] wrote:

quoted

quoted

(2) is what is happening in this case. fw_devlink=on sees that
"switch" implements the "switch_intc" and "switch" hasn't finished
probing yet. So it has no way of knowing that switch_intc is actually
ready. And even if switch_intc was registered as part of switch's
probe() by the time the PHYs are added, switch_intc could get
deregistered if the probe fails at a later point. So until probe()
returns 0, fw_devlink can't be fully sure the supplier (switch_intc)
is ready. Which is good in general because you won't have to
forcefully unbind (if that is even handled correctly in the first
place) the consumers of a device if it fails probe() half way through
registering a few services.

I had to read your email a couple of times before I understood it. I
think I do now, but apologies if I'm not making sense.

quoted

There are actually a few different circular references with the way
switches work. Take for example:

&fec1 {
        phy-mode = "rmii";
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_fec1>;
        status = "okay";

        fixed-link {
                speed = <100>;
                full-duplex;
        };

        mdio1: mdio {
                #address-cells = <1>;
                #size-cells = <0>;
                clock-frequency = <12500000>;
                suppress-preamble;
                status = "okay";

                switch0: switch0@0 {
                        compatible = "marvell,mv88e6190";
                        pinctrl-0 = <&pinctrl_gpio_switch0>;
                        pinctrl-names = "default";
                        reg = <0>;
                        eeprom-length = <65536>;
                        interrupt-parent = <&gpio3>;
                        interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
                        interrupt-controller;
                        #interrupt-cells = <2>;

                        ports {
                                #address-cells = <1>;
                                #size-cells = <0>;

                                port@0 {
                                        reg = <0>;
                                        label = "cpu";
                                        ethernet = <&fec1>;

                                        fixed-link {
                                                speed = <100>;
                                                full-duplex;
                                        };
                                };

FEC is an ethernet controller. It has an MDIO bus, and on the bus is
an Ethernet switch. port 0 of the Ethernet switch is connected to the
FEC ethernet controller.

While the FEC probes, it will at some point register its MDIO bus. At
that point, the MDIO bus is probed, the switch is found, and
registered with the switch core. The switch core looks for the port
with an ethernet property and goes looking for that ethernet
interface. But that this point in time, the FEC probe has only got as
far as registering the MDIO bus. The interface itself is not
registered. So finding the interface fails, and we go into
EPROBE_DEFER for probing the switch.

Ok, I understood up to here. Couple of questions:
Is this EPROBE_DEFER causing an issue? Wouldn't the switch then
probe successfully when it's reattempted? And then things work
normally? I don't see what the problem is.

Everything works on the second time around. So there is no problem,
other than we waste time trying to probe the switch, which we know is
going to fail. Depending on the setup, this can add 1/2 second to the
boot time. 

quoted

It is pretty hard to solve. An Ethernet interface can be used by the
kernel itself, e.g. NFS root. At the point you call register_netdev()
in the probe function, to register the interface with the core,

Are you using "ethernet interface" and "ethernet controller"
interchangeably?

Yeh, pretty much.

Looking at some other drivers, it looks like the
ethernet controlled (FEC) is what would call register_netdev(). So
what's wrong with that happening if switch0 has not probed
successfully?

quoted

it
needs to be fully ready to go.  The networking stack can start using
the interface before register_netdev() even returns. So you cannot
first register the interface and then register the MDIO bus.

I once looked to see if it was possible to tell the driver core to not
even bother probing a bus as soon as it is registered, go straight to
defer probe handling. Because this is one case we know it cannot
work. But it does not seem possible.

fw_devlink doesn't understand the "ethernet" property. If I add that,
then in the example you state above, switch0's probe won't even be
called until the FEC probe returns. The change is pretty trivial
(pasted below) -- can you try it out and tell me if it does what you
need/want?

Cool. I will try this.

Thanks
	Andrew