Re: [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@1 {
         };

         gmiitorgmii0: gmiitorgmii@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@1 {
         };

         gmiitorgmii0: gmiitorgmii@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