linux-kernel - Re: [PATCH 4/4] dt-bindings: PCI: microchip,pcie-host: fix missing address translation property

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Date:   Fri, 12 Aug 2022 10:52:02 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Conor Dooley <mail@...chuod.ie>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Greentime Hu <greentime.hu@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Conor Dooley <conor.dooley@...rochip.com>
Cc:     linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 4/4] dt-bindings: PCI: microchip,pcie-host: fix missing
 address translation property

On 11/08/2022 23:33, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@...rochip.com>
> 
> When the PCI controller node was added to the PolarFire SoC dtsi,
> dt-schema was not able to detect the presence of some undocumented
> properties due to how it handled unevaluatedProperties. v2022.08
> introduces better validation, producing the following error:
> 
> arch/riscv/boot/dts/microchip/mpfs-polarberry.dtb: pcie@...0000000: Unevaluated properties are not allowed ('clock-names', 'microchip,axi-m-atr0' were unexpected)
>         From schema: Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml
> 
> Fixes: 528a5b1f2556 ("riscv: dts: microchip: add new peripherals to icicle kit device tree")
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> ---
> I feel like there's a pretty good chance that this is not the way this
> should have been done and the property should be marked as deprecated
> but I don't know enough about PCI to answer that.

It seems bindings were added incomplete and now based on DTS (which did
not match bindings), we keep adding "missing" properties. I don't think
it is good. It creates a precedence where someone might intentionally
sneak limited bindings (without controversial property) and later claim
"I forgot to include foo,bar".

Therefore the property should pass review just like it is newly added
property.

> ---
>  .../devicetree/bindings/pci/microchip,pcie-host.yaml  | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml b/Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml
> index 9b123bcd034c..9ac34b33c4b2 100644
> --- a/Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml
> +++ b/Documentation/devicetree/bindings/pci/microchip,pcie-host.yaml
> @@ -71,6 +71,17 @@ properties:
>    msi-parent:
>      description: MSI controller the device is capable of using.
>  
> +  microchip,axi-m-atr0:

Name is not helping. If it is offset, add such suffix (see
brcm,iproc-pcie.yaml).

Unfortunately I don't know PCIe good enough to judge whether the
property makes any sense or some other ranges-style should be used.

> +    description: |
> +      Depending on the FPGA bitstream, the AXIM address translation table in the
> +      PCIe controllers bridge layer may need to be configured. Use this property
> +      to set the address offset. For more information, see Section 1.3.3,
> +      "PCIe/AXI4 Address Translation" of the PolarFire SoC PCIe User Guide:
> +      https://www.microsemi.com/document-portal/doc_download/1245812-polarfire-fpga-and-polarfire-soc-fpga-pci-express-user-guide
> +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> +    minItems: 2

minItems should not be needed, but you should instead describe the items
in the matrix.

> +    maxItems: 2


Best regards,
Krzysztof