linux-kernel - Re: [PATCH 1/2] dt-bindings:pci: Set LTSSM Detect.Quiet state delay.

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Date:   Tue, 9 Mar 2021 09:46:30 -0700
From:   Rob Herring <robh+dt@...nel.org>
To:     Nadeem Athani <nadeem@...ence.com>
Cc:     Tom Joseph <tjoseph@...ence.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        PCI <linux-pci@...r.kernel.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Milind Parab <mparab@...ence.com>,
        Swapnil Kashinath Jakhade <sjakhade@...ence.com>,
        Parshuram Raju Thombare <pthombar@...ence.com>
Subject: Re: [PATCH 1/2] dt-bindings:pci: Set LTSSM Detect.Quiet state delay.

On Tue, Mar 9, 2021 at 12:31 AM Nadeem Athani <nadeem@...ence.com> wrote:
>
> The parameter detect-quiet-min-delay can be used to program the minimum
> time that LTSSM waits on entering Detect.Quiet state.
> 00 : 0us minimum wait time in Detect.Quiet state.
> 01 : 100us minimum wait time in Detect.Quiet state.
> 10 : 1000us minimum wait time in Detect.Quiet state.
> 11 : 2000us minimum wait time in Detect.Quiet state.

What determines this setting? Is it per board or SoC? Is this a
standard PCI timing thing? Why does this need to be tuned per
platform?

> Signed-off-by: Nadeem Athani <nadeem@...ence.com>
> ---
>  .../devicetree/bindings/pci/cdns,cdns-pcie-host.yaml        | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
> index 293b8ec318bc..a1d56e0be419 100644
> --- a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
> +++ b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
> @@ -27,6 +27,18 @@ properties:
>
>    msi-parent: true
>
> +  detect-quiet-min-delay:
> +    description:
> +      LTSSM Detect.Quiet state minimum delay.
> +      00 : 0us minimum wait time
> +      01 : 100us minimum wait time
> +      10 : 1000us minimum wait time
> +      11 : 2000us minimum wait time
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    minimum: 0
> +    maximum: 3
> +    default: 0
> +
>  required:
>    - reg
>    - reg-names
> @@ -48,6 +60,7 @@ examples:
>              linux,pci-domain = <0>;
>              vendor-id = <0x17cd>;
>              device-id = <0x0200>;
> +            detect-quiet-min-delay = <0>;
>
>              reg = <0x0 0xfb000000  0x0 0x01000000>,
>                    <0x0 0x41000000  0x0 0x00001000>;
> --
> 2.15.0
>