Re: [PATCH 3/5] dt-bindings: pci: Document the NVIDIA Tegra264 PCIe controller

[Thierry Reding <thierry.reding@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 4742 bytes --]

On Thu, Mar 19, 2026 at 04:26:31PM -0500, Rob Herring wrote:
> On Thu, Mar 19, 2026 at 11:01 AM Thierry Reding
> <thierry.reding@kernel.org> wrote:
> >
> > From: Thierry Reding <treding@nvidia.com>
> >
> > The six PCIe controllers found on Tegra264 are of two types: one is used
> > for the internal GPU and therefore is not connected to a UPHY and the
> > remaining five controllers are typically routed to a PCI slot and have
> > additional controls for the physical link.
> >
> > While these controllers can be switched into endpoint mode, this binding
> > describes the root complex mode only.
> >
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> >  .../bindings/pci/nvidia,tegra264-pcie.yaml    | 92 +++++++++++++++++++
> >  1 file changed, 92 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pci/nvidia,tegra264-pcie.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/pci/nvidia,tegra264-pcie.yaml b/Documentation/devicetree/bindings/pci/nvidia,tegra264-pcie.yaml
> > new file mode 100644
> > index 000000000000..56d69de2788b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pci/nvidia,tegra264-pcie.yaml
> > @@ -0,0 +1,92 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/pci/nvidia,tegra264-pcie.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: NVIDIA Tegra264 PCIe controller
> > +
> > +maintainers:
> > +  - Thierry Reding <thierry.reding@gmail.com>
> > +  - Jon Hunter <jonathanh@nvidia.com>
> > +
> > +properties:
> > +  compatible:
> > +    const: nvidia,tegra264-pcie
> > +
> > +  reg:
> > +    minItems: 4
> > +    maxItems: 5
> > +
> > +  reg-names:
> > +    minItems: 4
> > +    maxItems: 5
> > +
> > +  interrupts:
> > +    minItems: 1
> > +    maxItems: 4
> > +
> > +  dma-coherent: true
> > +
> > +  nvidia,bpmp:
> > +    $ref: /schemas/types.yaml#/definitions/phandle-array
> > +    description: |
> > +      Must contain a pair of phandle (to the BPMP controller node) and
> > +      controller ID. The following are the controller IDs for each controller:
> > +
> > +      0: C0
> > +      1: C1
> > +      2: C2
> > +      3: C3
> > +      4: C4
> > +      5: C5
> > +    items:
> > +      - items:
> > +          - description: phandle to the BPMP controller node
> > +          - description: PCIe controller ID
> > +            maximum: 5
> > +
> > +unevaluatedProperties: false
> > +
> > +required:
> > +  - interrupt-map
> > +  - interrupt-map-mask
> > +  - iommu-map
> > +  - msi-map
> > +  - nvidia,bpmp
> > +
> > +allOf:
> > +  - $ref: /schemas/pci/pci-host-bridge.yaml#
> > +  - oneOf:
> > +    - description: C0 controller (no UPHY)
> > +      properties:
> > +        reg:
> > +          items:
> > +            - description: application layer registers
> > +            - description: transaction layer registers
> > +            - description: privileged transaction layer registers
> > +            - description: ECAM-compatible configuration space
> > +
> > +        reg-names:
> > +          items:
> > +            - const: xal
> > +            - const: xtl
> > +            - const: xtl-pri
> > +            - const: ecam
> > +
> > +    - description: C1-C5 controllers (with UPHY)
> > +      properties:
> > +        reg:
> > +          items:
> > +            - description: application layer registers
> > +            - description: transaction layer registers
> > +            - description: privileged transaction layer registers
> > +            - description: data link/physical layer registers
> > +            - description: ECAM-compatible configuration space
> > +
> > +      items:
> > +        - const: xal
> > +        - const: xtl
> > +        - const: xtl-pri
> > +        - const: xpl
> 
> Put this entry last since it is the optional one. Then you can move
> all of this to the top-level and get rid of the duplication.

I understand this concern and was actually on the fence about this
myself. The reason why I ultimately went with this variant is for two
reasons:

  1. XPL does not exist for controller 0, the variant above makes that
     very explicit. It explicitly documents that controller 0 is used
     for internal purposes and cannot be connected to an external port
     like the other five controllers.

  2. The ECAM region is part of a memory region specifically reserved
     for configuration space, whereas all of the other regions are
     from the controller's MMIO region. I find the DT hard to read if
     the two are interleaved.

Thierry

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]