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

Marek Behún
2022-01-05T14:14:52Z

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?

Marek