linux-kernel - Re: [PATCH V2 2/2] schemas: pci: bridge: Document PCIe N

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Message-ID: <CAL_JsqJE2x7XVkVKQuECTYfrML9V2TxdVNF-=EyTBbnGUEvhzw@mail.gmail.com>
Date: Fri, 24 Jan 2025 09:01:27 -0600
From: Rob Herring <robh@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: andersson@...nel.org, dmitry.baryshkov@...aro.org, 
	manivannan.sadhasivam@...aro.org, krzk@...nel.org, helgaas@...nel.org, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, 
	lpieralisi@...nel.org, kw@...ux.com, conor+dt@...nel.org, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
	devicetree-spec@...r.kernel.org, quic_vbadigan@...cinc.com
Subject: Re: [PATCH V2 2/2] schemas: pci: bridge: Document PCIe N_FTS

On Fri, Jan 24, 2025 at 4:11 AM Krishna Chaitanya Chundru
<krishna.chundru@....qualcomm.com> wrote:
>
> Per PCIe r6.0, sec 4.2.5.1, during Link training, a PCIe component
> captures the N_FTS value it receives.  Per 4.2.5.6, when
> transitioning the Link from L0s to L0, it must transmit N_FTS Fast
> Training Sequences to enable the receiver to obtain bit and Symbol
> lock.
>
> Components may have device-specific ways to configure N_FTS values
> to advertise during Link training.  Define an n_fts array with an
> entry for each supported data rate.
>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
>  dtschema/schemas/pci/pci-bus-common.yaml | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/dtschema/schemas/pci/pci-bus-common.yaml b/dtschema/schemas/pci/pci-bus-common.yaml
> index a9309af..968df43 100644
> --- a/dtschema/schemas/pci/pci-bus-common.yaml
> +++ b/dtschema/schemas/pci/pci-bus-common.yaml
> @@ -128,6 +128,15 @@ properties:
>      $ref: /schemas/types.yaml#/definitions/uint32
>      enum: [ 1, 2, 4, 8, 16, 32 ]
>
> +  n-fts:
> +    description:
> +      The number of Fast Training Sequences (N_FTS) required by the
> +      Receiver (this component) when transitioning the Link from L0s
> +      to L0; advertised during initial Link training
> +    $ref: /schemas/types.yaml#/definitions/uint8-array
> +    minItems: 1
> +    maxItems: 5

You still need to define what each entry is.

> +
>    reset-gpios:
>      description: GPIO controlled connection to PERST# signal
>      maxItems: 1
> --
> 2.34.1
>