[QUESTION] Device tree for gmii-to-rgmii phy driver

[Michal Simek]

Hi,

On 3/16/23 17:52, Stefan Herbrechtsmeier wrote:
> Hi Siva Durga Prasad Paladugu,
> 
> we want to add rgmii-id support to the gmiitorgmii phy driver. How does the 
> correct device tree for the gmiitorgmii looks like? The converter sits between 
> the MAC and the external PHY (MAC <==> GMII2RGMII <==> RGMII_PHY) which would 
> mean that the phy-handle of the MAC should point to the GMII2RGMII and the 
> GMII2RGMII to RGMII_PHY:
> 
> &gem0 {
>      phy-handle = <&gmiitorgmii0>;
>      phy-mode = "gmii";
> 
>      mdio {
>          ethphy0: ethernet-phy at 1 {
>          };
> 
>          gmiitorgmii0: gmiitorgmii at 8 {
>              compatible = "xlnx,gmii-to-rgmii-1.0";
>              phy-handle = <&ethphy0>;
>              phy-mode = "rgmii-id";
>          };
>      };
> };
> 
> This device tree snippet does not work in the kernel. The kernel gmii2rgmii 
> driver does not use a phy driver as base and manipulates the functions of the 
> external phy object instead. It requires the following device tree snippet:
> 
> &gem0 {
>      phy-handle = <&ethphy0>;
>      phy-mode = "rgmii-id";
> 
>      mdio {
>          ethphy0: ethernet-phy at 1 {
>          };
> 
>          gmiitorgmii0: gmiitorgmii at 8 {
>              compatible = "xlnx,gmii-to-rgmii-1.0";
>              phy-handle = <&ethphy0>;
>              phy-mode = "rgmii-id";
>          };
>      };
> };
> 
> This does not work in u-boot because the phy framework ignores the phy-handle of 
> the MAC for the gmii2rgmii but the gmii2rgmii driver itself checks the phy-mode 
> of the MAC.
> 
> What is the correct device tree and thereby proper implementation?

It is known issue for some time and U-Boot description is correct. Linux needs 
to be fixed. I remember there were any issue with framework not supporting it 
that's why unfortunately different description needs to be used.
I am CCing Harini. Here team should work on getting this fixed.

Thanks,
Michal