Re: [PATCH v2] schemas: pci: Document PCIe T_POWER_ON

[Krishna Chaitanya Chundru]

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@xxxxxxxxxxxxxxxx>
> > ---
> > Changes in v1:
> > - Updated the commiit text (Mani).
> > - Link to v1: https://lore.kernel.org/all/20251110112550.2070659-1-krishna.chundru@xxxxxxxxxxxxxxxx/#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