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

[Krishna Chaitanya Chundru]

On 1/6/2025 8:37 PM, Rob Herring wrote:
> On Mon, Jan 6, 2025 at 3:33 AM Krishna Chaitanya Chundru
> <krishna.chundru@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> > ---
> > - 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?
These applies to downstream ports also on a 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?
yes, nfts is the PCIe spec 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?
yes there are from Gen1 to Gen 5, I will update this in next patch these
details.
> > +    items:
> > +      maximum: 255
>
> Why not use uint8 array then?
In the previous commits it was suggested to use u32 by the reviewers to
make it uniform withall the properties,it makes sense to use it as uint8
as we are moving to generic properties.

- Krishna Chaitanya.

> > +
> >     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