Message-ID: <CAL_JsqJUzB71QdMcxJtNZ7raoPcK+SfTh7EVzGmk=syo8xLKQw@mail.gmail.com>
Date: Thu, 4 Dec 2025 11:09:09 -0600
From: Rob Herring <robh@...nel.org>
To: Andrea della Porta <andrea.porta@...e.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Jim Quinlan <jim2101024@...il.com>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, kwilczynski@...nel.org, 
	Manivannan Sadhasivam <mani@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rpi-kernel@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, iivanov@...e.de, svarbanov@...e.de, 
	mbrugger@...e.com, Jonathan Bell <jonathan@...pberrypi.com>, 
	Phil Elwell <phil@...pberrypi.com>, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] dt-bindings: pci: brcmstb: Add rp1-nexus node to fix DTC warning

On Mon, Sep 1, 2025 at 3:48 AM Andrea della Porta <andrea.porta@...e.com> wrote:
>
> Hi Krzysztof,
>
> On 08:50 Fri 22 Aug     , Krzysztof Kozlowski wrote:
> > On 21/08/2025 17:22, Andrea della Porta wrote:
> > > Hi Krzysztof,
> > >
> > > On 10:55 Tue 12 Aug     , Krzysztof Kozlowski wrote:
> > >> On 12/08/2025 10:50, Andrea della Porta wrote:
> > >>> The devicetree compiler is complaining as follows:
> > >>>
> > >>> arch/arm64/boot/dts/broadcom/rp1-nexus.dtsi:3.11-14.3: Warning (unit_address_vs_reg): /axi/pcie@...0120000/rp1_nexus: node has a reg or ranges property, but no unit name
> > >>> /home/andrea/linux-torvalds/arch/arm64/boot/dts/broadcom/bcm2712-rpi-5-b.dtb: pcie@...0120000: Unevaluated properties are not allowed ('rp1_nexus' was unexpected)
> > >>
> > >> Please trim the paths.
> > >
> > > Ack.
> > >
> > >>
> > >>>
> > >>> Add the optional node that fix this to the DT binding.
> > >>>
> > >>> Reported-by: kernel test robot <lkp@...el.com>
> > >>> Closes: https://lore.kernel.org/oe-kbuild-all/202506041952.baJDYBT4-lkp@intel.com/
> > >>> Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> > >>> ---
> > >>>  Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml | 9 +++++++++
> > >>>  1 file changed, 9 insertions(+)
> > >>>
> > >>> diff --git a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > >>> index 812ef5957cfc..7d8ba920b652 100644
> > >>> --- a/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > >>> +++ b/Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml
> > >>> @@ -126,6 +126,15 @@ required:
> > >>>  allOf:
> > >>>    - $ref: /schemas/pci/pci-host-bridge.yaml#
> > >>>    - $ref: /schemas/interrupt-controller/msi-controller.yaml#
> > >>> +  - if:
> > >>> +      properties:
> > >>> +        compatible:
> > >>> +          contains:
> > >>> +            const: brcm,bcm2712-pcie
> > >>> +    then:
> > >>> +      properties:
> > >>> +        rp1_nexus:
> > >>
> > >> No, you cannot document post-factum... This does not follow DTS coding
> > >> style.
> > >
> > > I think I didn't catch what you mean here: would that mean that
> > > we cannot resolve that warning since we cannot add anything to the
> > > binding?
> >
> > I meant, you cannot use a warning from the code you recently introduced
> > as a reason to use incorrect style.
> >
> > Fixing warning is of course fine and correct, but for the code recently
> > introduced and which bypassed ABI review it is basically like new review
> > of new ABI.
> >
> > This needs standard review practice, so you need to document WHY you
> > need such node. Warning is not the reason here why you are doing. If
> > this was part of original patchset, like it should have been, you would
> > not use some imaginary warning as reason, right?
> >
> > So provide reason why you need here this dedicated child, what is that
> > child representing.
>
> Ack.
>
> >
> > Otherwise I can suggest: drop the child and DTSO, this also solves the
> > warning...
>
> This would not fix the issue: it's the non overlay that needs the specific
> node. But I got the point, and we have a solution for that (see below).
>
> >
> > >
> > > Regarding rp1_nexus, you're right I guess it should be
> > > rp1-nexus as per DTS coding style.
> > >
> > >>
> > >> Also:
> > >>
> > >> Node names should be generic. See also an explanation and list of
> > >> examples (not exhaustive) in DT specification:
> > >> https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation
> > >
> > > In this case it could be difficult: we need to search for a DT node
> >
> > Search like in driver? That's wrong, you should be searching by compatible.
>
> Thanks for the hint. Searching by compatble is the solution.

No, it is not.

> >
> > > starting from the DT root and using generic names like pci@0,0 or
> > > dev@0,0 could possibly led to conflicts with other peripherals.
> > > That's why I chose a specific name.
> >
> > Dunno, depends what can be there, but you do not get a specific
> > (non-generic) device node name for a generic PCI device or endpoint.
>
> I would use 'port' instead of rp1-nexus. Would it work for you?

Do you still plan to fix this? This is broken far worse than just the node name.

The 'rp1_nexus' node is applied to the PCI host bridge. That's wrong
unless this is PCI rather than PCIe. There's the root port device in
between.

The clue that things are wrong are start in the driver here:

rp1_node = of_find_node_by_name(NULL, "rp1_nexus");
if (!rp1_node) {
  rp1_node = dev_of_node(dev);
  skip_ovl = false;
}

You should not need to do this nor care what the node name is. The PCI
core should have populated pdev->dev.of_node for you. If not, your DT
is wrong. Turn on CONFIG_PCI_DYNAMIC_OF_NODES and look at the
resulting PCI nodes. They should also match what the hierarchy looks
like with lspci. I don't recommend you rely on
CONFIG_PCI_DYNAMIC_OF_NODES, but statically populate the nodes in the
DT. First, CONFIG_PCI_DYNAMIC_OF_NODES is an under development thing
and I hope to get rid of the config option. Second, your case is
static (i.e. not a PCIe card in a slot) so there is no issue
hardcoding the DT.

As far as the node name, I don't care so much as long as the driver
doesn't care and you don't use '_' or 'pcie?' (that's for PCI
bridges).

And why do we have drivers/misc/rp1/rp1-pci.dtso and a .dtso in
arch/arm64? There should not be both.

Rob

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