Subject: Re: [net-next PATCH RFC v3 1/8] dt-bindings: net: document ethernet PHY package nodes

From: Christian Marangi <[email-masked]>
Date: Sun, 7 Jan 2024 22:45:17 +0100

On Sun, Jan 07, 2024 at 11:49:12PM +0200, Sergey Ryazanov wrote:
> Hi Christian,
> 
> On 07.01.2024 20:30, Christian Marangi wrote:
> > On Sun, Jan 07, 2024 at 08:00:33PM +0200, Sergey Ryazanov wrote:
> > > On 26.11.2023 03:53, Christian Marangi wrote:
> > > > Document ethernet PHY package nodes used to describe PHY shipped in
> > > > bundle of 4-5 PHY. The special node describe a container of PHY that
> > > > share common properties. This is a generic schema and PHY package
> > > > should create specialized version with the required additional shared
> > > > properties.
> > > > 
> > > > Example are PHY package that have some regs only in one PHY of the
> > > > package and will affect every other PHY in the package, for example
> > > > related to PHY interface mode calibration or global PHY mode selection.
> > > > 
> > > > The PHY package node MUST declare the base address used by the PHY driver
> > > > for global configuration by calculating the offsets of the global PHY
> > > > based on the base address of the PHY package and declare the
> > > > "ethrnet-phy-package" compatible.
> > > > 
> > > > Each reg of the PHY defined in the PHY package node is absolute and will
> > > > reference the real address of the PHY on the bus.
> > > > 
> > > > Signed-off-by: Christian Marangi <[email-masked]>
> > > > ---
> > > >    .../bindings/net/ethernet-phy-package.yaml    | 75 +++++++++++++++++++
> > > >    1 file changed, 75 insertions(+)
> > > >    create mode 100644 Documentation/devicetree/bindings/net/ethernet-phy-package.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/net/ethernet-phy-package.yaml b/Documentation/devicetree/bindings/net/ethernet-phy-package.yaml
> > > > new file mode 100644
> > > > index 000000000000..244d4bc29164
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/net/ethernet-phy-package.yaml
> > > > @@ -0,0 +1,75 @@
> > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/net/ethernet-phy-package.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Ethernet PHY Package Common Properties
> > > > +
> > > > +maintainers:
> > > > +  - Christian Marangi <[email-masked]>
> > > > +
> > > > +description:
> > > > +  This schema describe PHY package as simple container for
> > > > +  a bundle of PHYs that share the same properties and
> > > > +  contains the PHYs of the package themself.
> > > > +
> > > > +  Each reg of the PHYs defined in the PHY package node is
> > > > +  absolute and describe the real address of the PHY on the bus.
> > > > +
> > > > +properties:
> > > > +  $nodename:
> > > > +    pattern: "^ethernet-phy-package(@[a-f0-9]+)?$"
> > > > +
> > > > +  compatible:
> > > > +    const: ethernet-phy-package
> > > > +
> > > > +  reg:
> > > > +    minimum: 0
> > > > +    maximum: 31
> > > > +    description:
> > > > +      The base ID number for the PHY package.
> > > > +      Commonly the ID of the first PHY in the PHY package.
> > > > +
> > > > +      Some PHY in the PHY package might be not defined but
> > > > +      still exist on the device (just not attached to anything).
> > > > +      The reg defined in the PHY package node might differ and
> > > > +      the related PHY might be not defined.
> > > > +
> > > > +  '#address-cells':
> > > > +    const: 1
> > > > +
> > > > +  '#size-cells':
> > > > +    const: 0
> > > > +
> > > > +patternProperties:
> > > > +  ^ethernet-phy(@[a-f0-9]+)?$:
> > > > +    $ref: ethernet-phy.yaml#
> > > > +
> > > > +required:
> > > > +  - compatible
> > > > +  - reg
> > > > +
> > > > +additionalProperties: true
> > > > +
> > > > +examples:
> > > > +  - |
> > > > +    mdio {
> > > > +        #address-cells = <1>;
> > > > +        #size-cells = <0>;
> > > > +
> > > > +        ethernet-phy-package@16 {
> > > > +            #address-cells = <1>;
> > > > +            #size-cells = <0>;
> > > > +            compatible = "ethernet-phy-package";
> > > > +            reg = <0x16>;
> > > > +
> > > > +            ethernet-phy@16 {
> > > > +              reg = <0x16>;
> > > > +            };
> > > > +
> > > > +            phy4: ethernet-phy@1a {
> > > > +              reg = <0x1a>;
> > > > +            };
> > > > +        };
> > > > +    };
> > > 
> > > So, we ended up on a design where we use the predefined compatible string
> > > 'ethernet-phy-package' to recognize a phy package inside the
> > > of_mdiobus_register() function. During the V1 discussion, Vladimir came up
> > > with the idea of 'ranges' property usage [1]. Can we use 'ranges' to
> > > recognize a phy package in of_mdiobus_register()? IMHO this will give us a
> > > clear DT solution. I mean 'ranges' clearly indicates that child nodes are in
> > > the same address range as the parent node. Also we can list all child
> > > addresses in 'reg' to mark them occupied.
> > > 
> > >    mdio {
> > >      ...
> > > 
> > >      ethernet-phy-package@16 {
> > >        compatible = "qcom,qca8075";
> > >        reg = <0x16>, <0x17>, <0x18>, <0x19>, <0x1a>;
> > >        ranges;
> > >        ...
> > > 
> > >        ethernet-phy@16 {
> > >          reg = <0x16>;
> > >        };
> > > 
> > >        ethernet-phy@1a {
> > >          reg = <0x1a>;
> > >        };
> > >      };
> > >    };
> > > 
> > > Did you find some issues with the 'ranges' conception?
> > 
> > Nope it's ok but it might pose some confusion with the idea that the
> > very first element MUST be THE STARTING ADDR of the PHY package. (people
> > might think that it's just the list of the PHYs in the package and
> > remove the hardware unconnected ones... but that would be fault of who
> > write the DT anyway.)
> 
> Make sense. I do not insist on addresses listing. Mainly I'm thinking of a
> proper way to show that child nodes are accessible directly on the parent
> bus, and introducing the special compatibility string, while we already have
> the 'ranges' property.
> 
> But it's good to know Rob's opinion on whether it is conceptually right to
> use 'ranges' here.
>

I like the ideas of ranges and I will try to propose it... Another idea
might be declare something like <0x16 0x4> where the additional cell
would declare the amount of address occupiaed by the package. But I
think your way is much better and less ""custom"". Yes would also love
some feedback from Rob about this.

> > > And I would like to ask you about another issue raised by Vladimir [1].
> > > These phy chips become SoC with all these built-in PHYs, PCSs, clocks,
> > > interrupt controllers, etc. Should we address this now? Or should we go with
> > > the proposed solution for now and postpone modeling of other peripherals
> > > until we get a real hardware, as Andrew suggested?
> > 
> > Honestly I would postpone untile we have a clear idea of what is
> > actually part of the PHY and what can be handled externally... Example
> > setting the clock in gcc, writing a specific driver...
> > 
> > It's a random idea but maybe most of the stuff required for that PHY is
> > just when it's connected to a switch... In that case it would all be
> > handled in the switch driver (tobe extended qca8k) and all these extra
> > stuff would be placed in that node instead of bloating phy nodes with
> > all kind of clk and other stuff.
> > 
> > This series still require 2 more series (at803x splint and cleanup) to be
> > actually proposed so we have some time to better define this.
> > 
> > What do you think?
> 
> Fair enough! Let's postpone until we really need it. I noticed this
> PHY-like-SoC discussion in the V1 comments, and it was not finished there
> neither addressed in the latest patch comment. So I asked just to be sure
> that we were finished with this. Thank you for the clarification.
> 
> --
> Sergey
> 

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