Re: [PATCH net-next 03/12] dt-bindings: net: pcs: add bindings for Renesas RZ/N1 MII converter

Clément Léger
2022-04-21T07:38:24Z

Le Wed, 20 Apr 2022 15:11:26 -0500,
Rob Herring <robh@kernel.org> a écrit :

> On Tue, Apr 19, 2022 at 05:00:44PM +0200, Clément Léger wrote:
> > Le Tue, 19 Apr 2022 08:43:47 -0500,
> > Rob Herring <robh@kernel.org> a écrit :
> >
> > > > + clocks:
> > > > + items:
> > > > + - description: MII reference clock
> > > > + - description: RGMII reference clock
> > > > + - description: RMII reference clock
> > > > + - description: AHB clock used for the MII converter register interface
> > > > +
> > > > + renesas,miic-cfg-mode:
> > > > + description: MII mux configuration mode. This value should use one of the
> > > > + value defined in dt-bindings/net/pcs-rzn1-miic.h.
> > >
> > > Describe possible values here as constraints. At present, I don't see
> > > the point of this property if there is only 1 possible value and it is
> > > required.
> >
> > The ethernet subsystem contains a number of internal muxes that allows
> > to configure ethernet routing. This configuration option allows to set
> > the register that configure these muxes.
> >
> > After talking with Andrew, I considered moving to something like this:
> >
> > eth-miic@44030000 {
> > compatible = "renesas,rzn1-miic";
> >
> > mii_conv1: mii-conv-1 {
> > renesas,miic-input = <MIIC_GMAC1_PORT>;
> > port = <1>;
>
> 'port' is already used, find another name. Maybe 'reg' here. Don't know.
> What do 1 and 2 represent?

'port' represent the port index in the MII converter IP. I went with reg
first, but according to Andrew feedback, it looked like it was a bad
idea since it was not really a "bus". However, this pattern is already
used for dsa ports.

> > >
> > > Why do you need sub-nodes? They don't have any properties. A simple mask
> > > property could tell you which ports are present/active/enabled if that's
> > > what you are tracking. Or the SoC specific compatibles you need to add
> > > can imply the ports if they are SoC specific.
> >
> > The MACs are using phandles to these sub-nodes to query a specific MII
> > converter port PCS:
> >
> > switch@44050000 {
> > compatible = "renesas,rzn1-a5psw";
> >
> > ports {
> > port@0 {
>
> ethernet-ports and ethernet-port so we don't collide with the graph
> binding.

Acked.

>
>
> > reg = <0>;
> > label = "lan0";
> > phy-handle = <&switch0phy3>;
> > pcs-handle = <&mii_conv4>;
> > };
> > };
> > };
> >
> > According to Andrew, this is not a good idea to represent the PCS as a
> > bus since it is indeed not a bus. I could also switch to something like
> > pcs-handle = <&eth_mii 4> but i'm not sure what you'd prefer. We could
> > also remove this from the device-tree and consider each driver to
> > request the MII ouput to be configured using something like this for
> > instance:
>
> I'm pretty sure we already defined pcs-handle as only a phandle. If you
> want variable cells, then it's got to be extended like all the other
> properties using that pattern.

Yep, it seems to be used in some other driver as a single phandle too.
I'll kept that.

>
> >
> > miic_request_pcs(pcs_np, miic_port_nr, MIIC_SWITCHD_PORT);
> >
> > But I'm not really fan of this because it requires the drivers to
> > assume some specificities of the MII converter (port number are not in
> > the same order of the switch for instance) and thus I would prefer this
> > to be in the device-tree.
> >
> > Let me know if you can think of something that would suit you
> > better but keep in mind that I need to correctly match a switch/MAC
> > port with a PCS port and that I also need to configure MII internal
> > muxes.
> >
> > For more information, you can look at section 8 of the manual at [1].
>
> I can't really. Other people want their bindings reviewed too.

No worries.

>
> Rob

--
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin