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

On Mon, Oct 5, 2026 at 11:46 AM Conor Dooley [off-list ref] wrote:

On Sun, Oct 04, 2026 at 03:40:42PM +0100, Lucas Tanure wrote:

quoted

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 <redacted>
---
 .../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.

quoted

+
+        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