Re: [PATCH net-next 1/3] net: nixge: Add support for fixed-link subnodes

Moritz Fischer
2018-08-30T17:21:12Z

Hi Andrew,

On Wed, Aug 29, 2018 at 8:04 PM, Andrew Lunn <andrew@lunn.ch> wrote:
> On Wed, Aug 29, 2018 at 05:40:44PM -0700, Moritz Fischer wrote:
>> Add support for fixed-link cases where no MDIO is
>> actually required to run the device.
>> In that case no MDIO bus is instantiated since the
>> actual registers are not available in hardware.
>
> Hi Moritz
>
> There are a few different use cases here:
>
> The hardware is missing MDIO - You need fixed-link.

Agreed.
>
> The hardware has MDIO, but you don't have a PHY connected on it, and
> use fixed link.

Since it's an FPGA design in that case we'd probably build the hardware without
MDIO to save resources.

> The hardware has MDIO, and it is used e.g. for an Ethernet switch, or
> a PHY for another Ethernet interface. Plus you need fixed link.
We haven't had that yet but I can see that happen.
>
> The binding typically looks like:
>
> &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>;
> status = "okay";
>
> switch0: switch0@0 {
> compatible = "marvell,mv88e6085";
> pinctrl-names = "default";
> pinctrl-0 = <&pinctrl_switch>;
> reg = <0>;
> eeprom-length = <512>;
> interrupt-parent = <&gpio3>;
>
> It is important you have the mdio subnode, with PHYs and switches as
> children. The driver currently gets this wrong, it uses
> pdev->dev.of_node.

Oh, whoops. Yeah I should look into that. Any good examples of drivers doing
it right? Is the one going with the DT snippet above a good example?
>
> So the first patch should be to extend this behaviour. Look for a
> child node called mdio. If it exists, call nixge_mdio_setup() passing
> that child. Otherwise continue using pdev->dev.of_node, so you don't
> break backwards compatibility.

Ok will do.
>
> Then a patch adding support for fixed-link. If the mdio child node
> exists, you still need to register the MDIO bus. If there is no child
> node, but there is a fixed-link, skip registering the mdio bus with
> pdev->dev.of_node.
>
> Andrew

Thanks for your feedback, much appreciated!

Moritz