Re: [PATCH v2 net-next 2/7] dt-bindings: net: dsa: mediatek,mt7530: add passthrough mode

[Rob Herring <robh@kernel.org>]

On Thu, Sep 17, 2026 at 08:49:52PM +0000, netdev-bot+sashiko@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential
> issue(s) to consider:
> 
> Critical: 0 · High: 0 · Medium: 0 · Low: 2
> 
> - [Low] The added `description` paragraph in
>   Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml (lines…
> - [Low] Concern (retained for policy combination, assessed as a false
>   positive): the binding advertises a passthrough mode that…
> 
> --
> 
> dt-bindings: net: dsa: mediatek,mt7530: add passthrough mode
> 
> This adds a paragraph to the mediatek,mt7530 binding description explaining
> that MT7530/MT7531 switches can be operated in a "passthrough" mode where
> traffic moves unconditionally between the CPU port and a DSA link port to a
> second switch. The paragraph also states that in this mode the upstream
> switch may have no other ports or switch configuration.
> 
> > diff --git a/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml b/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml
> > index 90b3582b76190..e29fb86934981 100644
> > --- a/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml
> > +++ b/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml
> > @@ -73,6 +73,13 @@ description: |
> >  
> >        Check out example 7.
> >  
> > +  The MT7530 and MT7531 switches are capable of being operated in "passthrough"
> > +  mode. In this mode, traffic is unconditionally passed between the CPU port
> > +  and the DSA port which links to a second switch. To use passthrough mode, the
> > +  upstream switch is configured with a DSA link to the downstream switch. In
> > +  passthrough mode the upstream switch is restricted, with no other ports or
> > +  switch configuration allowed.
> > +
> 
> [Severity: Low]
> The last sentence states a hard device tree constraint, but it only exists
> as prose.  Should this restriction also be expressed in the
> machine-checkable part of the schema?

I don't know if that is possible.

> As it stands there is no new property, no if/then under allOf, and no $defs
> entry that limits the port set when a port carries a link phandle.  The port
> container in this same file is permissive:
> 
>   patternProperties:
>     "^(ethernet-)?ports$":
>       type: object
>       additionalProperties: true
> 
>       patternProperties:
>         "^(ethernet-)?port@[0-6]$":
>           type: object
>           additionalProperties: true
> 
> so a device tree describing an upstream MT7530/MT7531 with a CPU port, a DSA
> link port and extra user ports, plus gpio-controller/interrupt-controller,
> still passes dt_binding_check.  The layout is instead rejected at probe time
> by mt753x_check_passthrough() in drivers/net/dsa/mt7530.c, added by the
> following patch in the series:
> 
> 	if (passthrough_ports > 2 ||
> 	    (passthrough_ports == 2 && enabled_ports != 2)
> 	) {
> 		dev_err(dev, "Only two ports allowed in passthrough mode\n");
> 		return -EINVAL;
> 
> Two smaller points on the same paragraph:
> 
> Every other topology description in this description block ends with a
> pointer to a validated example ("Check out example 7." just above).  Could
> this one gain an example too, so the passthrough layout is actually exercised
> by dt_binding_check?

We don't really want more examples if there are actual .dts files 
upstream.

Rob