RE: [RFC PATCH v2 1/4] Documentation: DT: net: Add Xilinx gmiitorgmii converter device tree binding documentation

From: Appana Durga Kedareswara Rao
Date: Tue Jul 26 2016 - 11:09:34 EST


Hi Andrew,

Thanks for the inputs...

> >
> > > > Hi Kedareswara
> > > >
> > > > So looking at the device tree, you have the gmiitorgmii as an mdio
> > > > device. It will get probed as an mdio device, and from that you
> > > > know the address on the bus. However, your driver does not
> > > > actually do this. xilinx_gmii2rgmii.c is just a library of two
> > > > functions, and does not use any of this device tree information.
> > > > You device tree binding is completely bogus.
> > > >
> > > > What i think is a much more logical structure, and fits the
> > > > hardware, which is what DT is all about, is to make your driver an mdio
> driver.
> > > > Also, have a phy-handle pointing to the PHY in the gmii_to_rgmii node.
> > > > You then no longer need the exported gmii2rgmii_phyprobe() function.
> > > >
> > > > Next, you want gmiitorgmii driver to register a phy. The MAC
> > > > driver can then look this up using phy-handle:
> > > >
> > > > mdio {
> > > > #address-cells = <1>;
> > > > #size-cells = <0>;
> > > >
> > > > phy: ethernet-phy@0 {
> > > > reg = <0>;
> > > > };
> > > >
> > > > gmii_to_rgmii: gmii-to-rgmii@8 {
> > > > compatible = "xlnx,gmiitorgmii";
> > > > reg = <8>;
> > > > phy-handle = <&phy>;
> > > > };
> > > > };
> > >
> > >
> > > Thanks for your inputs initially we too thought the similar
> > > implementation But the GMII2RGMII converter contains only one
> > > register and it is not compatible to the standard ethernet MII
> > > interface. Also it doesn't have a standard VID and PID registers So,
> > > during the mdio bus scan, this device
> > will
> > > not appear.

I tried to implement the driver as you suggested but there are few limitations in this
Implementation please correct me if my understanding is wrong...

The device-tree will look like below...
mdio {
#address-cells = <1>;
#size-cells = <0>;
phy: ethernet-phy@0 {
reg = <0>;
};
gmii_to_rgmii: gmii-to-rgmii@8 {
compatible = "xlnx,gmiitorgmii";
reg = <8>;
phy-handle = <&phy>;
};
};

The MAC driver does the below.
---> It creates a MDIO device for the gmii_to_rgmii node.
---> It creates a PHY device for the External PHY node.

The GMII2RGMII driver does the below.
1) It registers the gmii_to_rgmii node as a MDIO driver.
It contains the external phy as a phy-handle
2) Register a PHY Driver.
---> Register it as a phy driver (phy_register_driver):
For this implementation the converter won't have any VID or DID(PHY register 2 and 3)
---> Register phy using of_phy_connect call:
For this implementation needed a netdev pointer to pass it to the of_phy_connect call.
(Need to allocate a network device during probe and need to register it as netdev)

For the 2nd one implement I am facing above limitations...
Please correct me if my understanding is wrong...

Regards,
Kedar.