Re: [RFC PATCH 2/6] dt-bindings: net: amlogic,meson-dwmac: add amlogic,t7-dwmac

[Lucas Tanure]

On Mon, Oct 5, 2026 at 11:46 AM Conor Dooley <conor@xxxxxxxxxx> wrote:
>
> On Sun, Oct 04, 2026 at 03:40:42PM +0100, Lucas Tanure wrote:
> > The T7 has the same ethernet glue as the G12A, but the controller
> > reaches DRAM through a pipeline stage that the hardware design inserts
> > in the bus path. That stage has a gate of its own, which no other member
> > of the family has. Nothing else in Linux claims the gate, so it is
> > switched off as unused and the port can then no longer complete a
> > transfer.
> >
> > Describing it means a fourth clock, and the fourth clock of the existing
> > list is the one driving the timing adjustment logic. The T7 applies the
> > RGMII RX delay through PRG_ETH1 and never enables that logic, so it has
> > no use for that clock. Give the T7 a list of its own with the pipeline
> > gate as the fourth entry, under the same name the SD/eMMC controllers of
> > this SoC already use for the equivalent stage on their own bus path. All
> > four entries are required, since the port cannot move data without any
> > of them.
> >
> > The RX delay range is the one the G12A has, since it is the same
> > register field.
> >
> > The compatible pairs the T7 name with the 5.10a Synopsys core the MAC
> > reports, and with the generic fallback.
> >
> > Assisted-by: LLM
> > Signed-off-by: Lucas Tanure <tanure@xxxxxxxxx>
> > ---
> >  .../bindings/net/amlogic,meson-dwmac.yaml     | 47 +++++++++++++++++++
> >  1 file changed, 47 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/net/amlogic,meson-dwmac.yaml b/Documentation/devicetree/bindings/net/amlogic,meson-dwmac.yaml
> > index 90ef79161ab1..96118b4d1560 100644
> > --- a/Documentation/devicetree/bindings/net/amlogic,meson-dwmac.yaml
> > +++ b/Documentation/devicetree/bindings/net/amlogic,meson-dwmac.yaml
> > @@ -23,6 +23,7 @@ select:
> >            - amlogic,meson-gxbb-dwmac
> >            - amlogic,meson-axg-dwmac
> >            - amlogic,meson-g12a-dwmac
> > +          - amlogic,t7-dwmac
> >    required:
> >      - compatible
> >
> > @@ -57,6 +58,47 @@ allOf:
> >              - const: clkin1
> >              - const: timing-adjustment
> >
> > +  # The T7 applies the RGMII RX delay through PRG_ETH1 and never enables the
> > +  # timing adjustment logic, so it has no timing-adjustment clock. What it does
> > +  # need is the gate of the pipeline stage the controller reaches DRAM through.
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            const: amlogic,t7-dwmac
> > +    then:
> > +      properties:
> > +        clocks:
> > +          items:
> > +            - description: GMAC main clock
> > +            - description: First parent clock of the internal mux
> > +            - description: Second parent clock of the internal mux
> > +            - description:
> > +                clock of the pipeline stage inserted in the bus path between
> > +                the controller and the DRAM. Without it, the controller cannot
> > +                complete DMA transfers.
>
> Have you checked that this actually works as a limiter to only 4 clocks?
I have now, and it does limit to four. Adding
a fifth clock to the board gets rejected:

  ethernet@fdc00000 (amlogic,t7-dwmac): clock-names:
    ['stmmaceth', 'clkin0', 'clkin1', 'pipeline', 'bogus'] is too long


> There's an additionalItems: true in the snps,dwmac.yaml that I don't
> know if will permit random additional items here.
There are two checks on clocks and both have to pass: snps,dwmac.yaml
allows 1 to 10 items, the t7 branch allows exactly 4. The
additionalItems: true only relaxes the first one, so the second still
rejects a fifth clock. The "exactly 4" is not something I wrote -
dt-schema's _fixup_items_size() sets minItems and maxItems from the
length of the items list.

>
> Cheers,
> Conor.
>
> > +
> > +        clock-names:
> > +          items:
> > +            - const: stmmaceth
> > +            - const: clkin0
> > +            - const: clkin1
> > +            - const: pipeline
> > +
> > +  # Delay definitions for Meson8b and newer (including T7)
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - amlogic,meson8b-dwmac
> > +              - amlogic,meson8m2-dwmac
> > +              - amlogic,meson-gxbb-dwmac
> > +              - amlogic,meson-axg-dwmac
> > +              - amlogic,meson-g12a-dwmac
> > +              - amlogic,t7-dwmac
> > +    then:
> > +      properties:
> >          amlogic,tx-delay-ns:
> >            enum: [0, 2, 4, 6]
> >            default: 2
> > @@ -106,6 +148,7 @@ allOf:
> >            contains:
> >              enum:
> >                - amlogic,meson-g12a-dwmac
> > +              - amlogic,t7-dwmac
> >      then:
> >        properties:
> >          rx-internal-delay-ps:
> > @@ -143,6 +186,10 @@ properties:
> >                - amlogic,meson6-dwmac
> >                - amlogic,meson8m2-dwmac
> >            - const: snps,dwmac
> > +      - items:
> > +          - const: amlogic,t7-dwmac
> > +          - const: snps,dwmac-5.10a
> > +          - const: snps,dwmac
> >
> >    reg:
> >      items:
> > --
> > 2.56.0
> >