linux-kernel - Re: [PATCH v2] schemas: pci: Document PCIe T_POWER

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Message-ID: <9dbae7ca-b24f-4591-99cf-7720ace6a452@oss.qualcomm.com>
Date: Thu, 13 Nov 2025 13:18:04 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: andersson@...nel.org, robh@...nel.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] schemas: pci: Document PCIe T_POWER_ON



On 11/10/2025 5:33 PM, Manivannan Sadhasivam wrote:
> On Mon, Nov 10, 2025 at 04:59:47PM +0530, Krishna Chaitanya Chundru wrote:
>>  From PCIe r6, 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 for each Root Port.
>>
> I'm not sure if we should restrict this property to just Root Ports. Defining a
> property in 'pci-bus-common.yaml' means, all PCI bridges could use it, but this
> value is applicable to endpoint devices also.
Better to add in pci-device.yaml then.
> Also, you might want to add some info that the driver (or DT consumer) should
> derive the T_POWER_ON Scale and T_POWER_ON Value from this value.
ack

- Krishna Chaitanya.
> - Mani
>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....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-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 5257339..bbe5510 100644
>> --- a/dtschema/schemas/pci/pci-bus-common.yaml
>> +++ b/dtschema/schemas/pci/pci-bus-common.yaml
>> @@ -152,6 +152,15 @@ properties:
>>         This property is invalid in host bridge nodes.
>>       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 r6.0, sec 5.5.4).
>> +
>>     supports-clkreq:
>>       description:
>>         If present this property specifies that CLKREQ signal routing exists from
>> -- 
>> 2.34.1
>>
>>