linux-kernel - Re: [PATCH v4 1/2] dt-bindings: pci: Retrain Link to work around Gen2 training defect.

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Date:   Fri, 11 Dec 2020 11:02:26 -0600
From:   Rob Herring <robh@...nel.org>
To:     Nadeem Athani <nadeem@...ence.com>
Cc:     Tom Joseph <tjoseph@...ence.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        devicetree@...r.kernel.org, Milind Parab <mparab@...ence.com>,
        Swapnil Kashinath Jakhade <sjakhade@...ence.com>,
        pthombar@...ence.com
Subject: Re: [PATCH v4 1/2] dt-bindings: pci: Retrain Link to work around Gen2
 training defect.

On Fri, Dec 11, 2020 at 9:03 AM Nadeem Athani <nadeem@...ence.com> wrote:
>
> Cadence controller will not initiate autonomous speed change if strapped as
> Gen2. The Retrain Link bit is set as quirk to enable this speed change.
> Adding a quirk flag based on a new compatible string.
>
> Signed-off-by: Nadeem Athani <nadeem@...ence.com>
> ---
>  Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
> index 293b8ec318bc..204d78f9efe3 100644
> --- a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
> +++ b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
> @@ -15,7 +15,9 @@ allOf:
>
>  properties:
>    compatible:
> -    const: cdns,cdns-pcie-host
> +    enum:
> +        - cdns,cdns-pcie-host
> +        - cdns,cdns-pcie-host-quirk-retrain

So, we'll just keep adding quirk strings on to the compatible? I don't
think so. Compatible strings should map to a specific
implementation/platform and quirks can then be implied from them. This
is the only way we can implement quirks in the OS without firmware
(DT) changes.

Rob