linux-kernel - Re: [PATCH v2 01/13] dt-bindings: pci: apple,pcie: Add t6020 compatible string

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Message-Id: <87ecyl6rtw.fsf@bloch.sibelius.xs4all.nl>
Date: Tue, 25 Mar 2025 16:41:15 +0100
From: Mark Kettenis <mark.kettenis@...all.nl>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	asahi@...ts.linux.dev, alyssa@...enzweig.io, j@...nau.net,
	marcan@...can.st, sven@...npeter.dev, bhelgaas@...gle.com,
	lpieralisi@...nel.org, kw@...ux.com,
	manivannan.sadhasivam@...aro.org, robh@...nel.org,
	krzk+dt@...nel.org
Subject: Re: [PATCH v2 01/13] dt-bindings: pci: apple,pcie: Add t6020 compatible string

> Date: Tue, 25 Mar 2025 11:02:30 +0000
> From: Marc Zyngier <maz@...nel.org>

Hi Marc,

> Hi Mark,
> 
> On Tue, 25 Mar 2025 10:50:18 +0000,
> Mark Kettenis <mark.kettenis@...all.nl> wrote:
> > 
> > > From: Marc Zyngier <maz@...nel.org>
> > > Date: Tue, 25 Mar 2025 10:25:58 +0000
> > 
> > Hi Marc,
> > 
> > Sorry for not spotting this in the earlier versions, but:
> 
> No worries -- I expected issues in that department.
> 
> >
> > > From: Alyssa Rosenzweig <alyssa@...enzweig.io>
> > > 
> > > t6020 adds some register ranges compared to t8103, so requires
> > > a new compatible as well as the new PHY registers themselves.
> > > 
> > > Signed-off-by: Alyssa Rosenzweig <alyssa@...enzweig.io>
> > > [maz: added PHY registers]
> > > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > > ---
> > >  Documentation/devicetree/bindings/pci/apple,pcie.yaml | 11 ++++++++++-
> > >  1 file changed, 10 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/pci/apple,pcie.yaml b/Documentation/devicetree/bindings/pci/apple,pcie.yaml
> > > index c8775f9cb0713..77554899b9420 100644
> > > --- a/Documentation/devicetree/bindings/pci/apple,pcie.yaml
> > > +++ b/Documentation/devicetree/bindings/pci/apple,pcie.yaml
> > > @@ -17,6 +17,10 @@ description: |
> > >    implements its root ports.  But the ATU found on most DesignWare
> > >    PCIe host bridges is absent.
> > >  
> > > +  On systems derived from T602x, the PHY registers are in a region
> > > +  separate from the port registers. In that case, there is one PHY
> > > +  register range per port register range.
> > > +
> > >    All root ports share a single ECAM space, but separate GPIOs are
> > >    used to take the PCI devices on those ports out of reset.  Therefore
> > >    the standard "reset-gpios" and "max-link-speed" properties appear on
> > > @@ -35,11 +39,12 @@ properties:
> > >            - apple,t8103-pcie
> > >            - apple,t8112-pcie
> > >            - apple,t6000-pcie
> > > +          - apple,t6020-pcie
> > >        - const: apple,pcie
> > 
> > Since the T602x PCIe controller has a different register layout, it
> > isn't compatible with the others, so it should not include the
> > "apple,pcie" compatible.  The "downstream" device trees for
> > T602x-based devices do indeed not list "apple,pcie" as a compatible.
> > So I think this needs to be written as:
> > 
> >   compatible:
> >     oneOf:
> >       - items:
> >           - enum:
> >               - apple,t8103-pcie
> >               - apple,t8112-pcie
> >               - apple,t6000-pcie
> >           - const: apple,pcie
> >       - const: apple,t6020-pcie
> 
> Ah, indeed, that's a good point. Thanks for that.
> 
> Whilst I have your attention, how about my question below:
> 
> >
> > >  
> > >    reg:
> > >      minItems: 3
> > > -    maxItems: 6
> > > +    maxItems: 10
> > >  
> > >    reg-names:
> > >      minItems: 3
> > > @@ -50,6 +55,10 @@ properties:
> > >        - const: port1
> > >        - const: port2
> > >        - const: port3
> > > +      - const: phy0
> > > +      - const: phy1
> > > +      - const: phy2
> > > +      - const: phy3
> 
> Do we need to make this t6020 specific?
> 
> Obviously, separate PHY registers do not make much sense before t6020,
> but I couldn't find a way to describe that. I don't even know if
> that's a desirable outcome.

I don't think there is a way to do that other than creating a separate
binding for t6020.  But I'm far from a dt-schema expert.  Maybe robh
has some advice here.