linux-kernel - Re: [PATCH V1] schemas: pci: bridge: Document PCI L0s & L1 entry delay and nfts

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Message-ID: <CAL_JsqJXGUmzE+tPccDmdi5r0YvQ5kOL2mh3e6KtEvTnsexnyg@mail.gmail.com>
Date: Mon, 6 Jan 2025 09:07:22 -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 V1] schemas: pci: bridge: Document PCI L0s & L1 entry
 delay and nfts

On Mon, Jan 6, 2025 at 3:33 AM Krishna Chaitanya Chundru
<krishna.chundru@....qualcomm.com> wrote:
>
> Some controllers and endpoints provide provision to program the entry
> delays of L0s & L1 which will allow the link to enter L0s & L1 more
> aggressively to save power.
>
> As per PCIe spec 6 sec 4.2.5.6, the number of Fast Training Sequence (FTS)
> can be programmed by the controllers or endpoints that is used for bit and
> Symbol lock when transitioning from L0s to L0 based upon the PCIe data rate
> FTS value can vary. So define a array for each data rate for nfts.
>
> These values needs to be programmed before link training.
>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
> - This change was suggested in this patch: https://lore.kernel.org/all/20241211060000.3vn3iumouggjcbva@thinkpad/
> ---
>  dtschema/schemas/pci/pci-bus-common.yaml | 16 ++++++++++++++++

Do these properties apply to any link like downstream ports on a PCIe switch?

>  1 file changed, 16 insertions(+)
>
> diff --git a/dtschema/schemas/pci/pci-bus-common.yaml b/dtschema/schemas/pci/pci-bus-common.yaml
> index 94b648f..f0655ba 100644
> --- a/dtschema/schemas/pci/pci-bus-common.yaml
> +++ b/dtschema/schemas/pci/pci-bus-common.yaml
> @@ -128,6 +128,16 @@ properties:
>      $ref: /schemas/types.yaml#/definitions/uint32
>      enum: [ 1, 2, 4, 8, 16, 32 ]
>
> +  nfts:

Kind of short. How about num-fts? Or is "NFTS" a PCI term?

> +    description:
> +      Number of Fast Training Sequence (FTS) used during L0s to L0 exit for bit
> +      and Symbol lock.
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +    minItems: 1
> +    maxItems: 5

Need to define what is each entry? Gen 1 to 5?

> +    items:
> +      maximum: 255

Why not use uint8 array then?

> +
>    reset-gpios:
>      description: GPIO controlled connection to PERST# signal
>      maxItems: 1
> @@ -150,6 +160,12 @@ properties:
>      description: Disables ASPM L0s capability
>      type: boolean
>
> +  aspm-l0s-entry-delay-ns:
> +    description: Aspm l0s entry delay.
> +
> +  aspm-l1-entry-delay-ns:
> +    description: Aspm l1 entry delay.
> +
>    vpcie12v-supply:
>      description: 12v regulator phandle for the slot
>
> --
> 2.34.1
>
>