linux-kernel - Re: [PATCH v3] schemas: pci: Document PCIe T_POWER

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Message-ID: <20251126144409.GA2825768@bhelgaas>
Date: Wed, 26 Nov 2025 08:44:09 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: andersson@...nel.org, robh@...nel.org, mani@...nel.org, krzk@...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,
	lukas@...ner.de
Subject: Re: [PATCH v3] schemas: pci: Document PCIe T_POWER_ON

On Wed, Nov 26, 2025 at 04:01:12PM +0530, Krishna Chaitanya Chundru wrote:
> From PCIe r7, sec 5.5.4 & Table 5-11 in sec 5.5.5 T_POWER_ON is the
> minimum amount of time(in us) that each component must wait in L1.2.Exit
> after sampling CLKREQ# asserted before actively driving the interface to
> ensure no device is ever actively driving into an unpowered component and
> these values are based on the components and AC coupling capacitors used
> in the connection linking the two components.
> 
> This property should be used to indicate the T_POWER_ON and drivers using
> this property are responsible for parsing both the scale and the value of
> T_POWER_ON to comply with the PCIe specification.

Add space before open "(" above and in description below.

> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
> Changes in v2:
> - Move the property to pci-device.yaml so that it will be applicable to
>   endpoint devices also (Mani).
> - Use latest spec (Lukas)
> - Link to v2: https://lore.kernel.org/all/20251110112947.2071036-1-krishna.chundru@oss.qualcomm.com/
> Changes in v1:
> - Updated the commiit text (Mani).
> - Link to v1: https://lore.kernel.org/all/20251110112550.2070659-1-krishna.chundru@oss.qualcomm.com/#t
> 
>  dtschema/schemas/pci/pci-device.yaml | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/dtschema/schemas/pci/pci-device.yaml b/dtschema/schemas/pci/pci-device.yaml
> index ca094a0..4baab71 100644
> --- a/dtschema/schemas/pci/pci-device.yaml
> +++ b/dtschema/schemas/pci/pci-device.yaml
> @@ -63,6 +63,15 @@ properties:
>      description: GPIO controlled connection to WAKE# signal
>      maxItems: 1
>  
> +  t-power-on-us:
> +    description:
> +      The minimum amount of time that each component must wait in
> +      L1.2.Exit after sampling CLKREQ# asserted before actively driving
> +      the interface to ensure no device is ever actively driving into an
> +      unpowered component. This value is based on the components and AC
> +      coupling capacitors used in the connection linking the two
> +      components(PCIe r7.0, sec 5.5.4).
> +
>  required:
>    - reg
>  
> -- 
> 2.34.1
>