linux-kernel - Re: [PATCH v3 04/17] dt-bindings: PCI: dwc: Add max-link-speed common property

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Date:   Wed, 15 Jun 2022 08:55:50 -0600
From:   Rob Herring <robh@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/17] dt-bindings: PCI: dwc: Add max-link-speed
 common property

On Fri, Jun 10, 2022 at 11:56:52AM +0300, Serge Semin wrote:
> In accordance with [1] DW PCIe controllers support up to Gen5 link speed.
> Let's add the max-link-speed property upper bound to 5 then. The DT
> bindings of the particular devices are expected to setup more strict
> constraint on that parameter.
> 
> [1] Synopsys DesignWare Cores PCI Express Controller Databook, Version
> 5.40a, March 2019, p. 27
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> ---
> 
> Changelog v3:
> - This is a new patch unpinned from the next one:
>   https://lore.kernel.org/linux-pci/20220503214638.1895-2-Sergey.Semin@baikalelectronics.ru/
>   by the Rob' request. (@Rob)
> ---
>  Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml | 3 +++
>  Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml     | 2 ++
>  Documentation/devicetree/bindings/pci/snps,dw-pcie.yaml        | 1 +
>  3 files changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml b/Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml
> index 627a5d6625ba..b2fbe886981b 100644
> --- a/Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml
> +++ b/Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml
> @@ -45,6 +45,9 @@ properties:
>        the peripheral devices available on the PCIe bus.
>      maxItems: 1
>  
> +  max-link-speed:
> +    maximum: 5

Unless the default is less than the max, shouldn't the max here be 1 
less than the h/w max?

> +
>    num-lanes:
>      description:
>        Number of PCIe link lanes to use. Can be omitted should the already
> diff --git a/Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml b/Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml
> index dcd521aed213..fc3b5d4ac245 100644
> --- a/Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml
> +++ b/Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml
> @@ -55,4 +55,6 @@ examples:
>  
>        phys = <&pcie_phy0>, <&pcie_phy1>, <&pcie_phy2>, <&pcie_phy3>;
>        phy-names = "pcie0", "pcie1", "pcie2", "pcie3";
> +
> +      max-link-speed = <3>;
>      };
> diff --git a/Documentation/devicetree/bindings/pci/snps,dw-pcie.yaml b/Documentation/devicetree/bindings/pci/snps,dw-pcie.yaml
> index 4a5c8b933b52..01cedf51e0f8 100644
> --- a/Documentation/devicetree/bindings/pci/snps,dw-pcie.yaml
> +++ b/Documentation/devicetree/bindings/pci/snps,dw-pcie.yaml
> @@ -74,4 +74,5 @@ examples:
>        phy-names = "pcie";
>  
>        num-lanes = <1>;
> +      max-link-speed = <3>;

This should give you an error because pci-bus.yaml only goes up to 4. 

I'm not really sure that limiting it in the common schema is too useful. 
We're going to be updating it one step at a time. Limiting it is really 
only helpful for specific implementations.

Patch 1 didn't apply for me, so none of the checks ran.

Rob