Re: [PATCH dt + pci 1/2] dt-bindings: Add 'slot-power-limit-milliwatt' PCIe port property

Pali Rohár
2022-01-05T15:14:17Z

On Wednesday 05 January 2022 08:27:21 Rob Herring wrote:
> On Wed, Jan 5, 2022 at 8:14 AM Marek Behún <kabel@kernel.org> wrote:
> >
> > On Fri, 12 Nov 2021 09:25:20 -0600
> > Rob Herring <robh@kernel.org> wrote:
> >
> > > On Sun, Oct 31, 2021 at 04:07:05PM +0100, Marek Behún wrote:
> > > > From: Pali Rohár <pali@kernel.org>
> > > >
> > > > This property specifies slot power limit in mW unit. It is a form-factor
> > > > and board specific value and must be initialized by hardware.
> > > >
> > > > Some PCIe controllers delegate this work to software to allow hardware
> > > > flexibility and therefore this property basically specifies what should
> > > > host bridge program into PCIe Slot Capabilities registers.
> > > >
> > > > The property needs to be specified in mW unit instead of the special format
> > > > defined by Slot Capabilities (which encodes scaling factor or different
> > > > unit). Host drivers should convert the value from mW to needed format.
> > > >
> > > > Signed-off-by: Pali Rohár <pali@kernel.org>
> > > > Signed-off-by: Marek Behún <kabel@kernel.org>
> > > > ---
> > > > Documentation/devicetree/bindings/pci/pci.txt | 6 ++++++
> > > > 1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
> > > > index 6a8f2874a24d..7296d599c5ac 100644
> > > > --- a/Documentation/devicetree/bindings/pci/pci.txt
> > > > +++ b/Documentation/devicetree/bindings/pci/pci.txt
> > > > @@ -32,6 +32,12 @@ driver implementation may support the following properties:
> > > > root port to downstream device and host bridge drivers can do programming
> > > > which depends on CLKREQ signal existence. For example, programming root port
> > > > not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
> > > > +- slot-power-limit-miliwatt:
> > >
> > > Typo.
> > >
> > > But we shouldn't be adding to pci.txt. This needs to go in the
> > > schema[1]. Patch to devicetree-spec list or GH PR is fine.
> >
> > Hello Rob,
> >
> > Pali's PR draft https://github.com/devicetree-org/dt-schema/pull/64
> > looks like it's going to take some time to work out.
> >
> > In the meantime, is it possible to somehow get the
> > slot-power-limit-milliwatt property merged into pci.txt so that we can start
> > putting it into existing device-trees?
> >
> > Or would it break dt_bindings_check if it isn't put into dt-schema's
> > pci-bus.yaml?
> >
> > Or should we simply put it into current version of pci-bus.yaml and
> > work out the split proposed by Pali's PR afterwards?
>
> In the existing pci-bus.yaml is fine.

Hello Rob! I do not think that it is possible to add this property
correctly in to the existing pci-bus.yaml file. As this file is not
prepared for slot properties. And I guess that adding new property at
"random" place is against the idea of schema validation (that validation
procedure accepts only valid DTS files).