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

From: Rob Herring <robh@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Marek Behún" <kabel@kernel.org>,
	devicetree@vger.kernel.org, PCI <linux-pci@vger.kernel.org>,
	"Bjorn Helgaas" <helgaas@kernel.org>
Subject: Re: [PATCH dt + pci 1/2] dt-bindings: Add 'slot-power-limit-milliwatt' PCIe port property
Date: Fri, 12 Nov 2021 14:56:26 -0600	[thread overview]
Message-ID: <CAL_Jsq+0ByuPqGw0L94qJktMy+J2XyGUQ1ZRjkBoMGX+ggBizw@mail.gmail.com> (raw)
In-Reply-To: <20211112171249.46xmj5zo3svm4qn2@pali>

On Fri, Nov 12, 2021 at 11:12 AM Pali Rohár <pali@kernel.org> wrote:
>
> On Friday 12 November 2021 10:30:01 Rob Herring wrote:
> > On Fri, Nov 12, 2021 at 9:32 AM Pali Rohár <pali@kernel.org> wrote:
> > >
> > > On Friday 12 November 2021 09:25:20 Rob Herring wrote:
> > > > On Sun, Oct 31, 2021 at 04:07:05PM +0100, Marek Behún wrote:
> > > > > +   If present, this property specifies slot power limit in milliwatts. Host
> > > > > +   drivers can parse this property and use it for programming Root Port or host
> > > > > +   bridge, or for composing and sending PCIe Set_Slot_Power_Limit messages
> > > > > +   through the Root Port or host bridge when transitioning PCIe link from a
> > > > > +   non-DL_Up Status to a DL_Up Status.
> > > >
> > > > If your slots are behind a switch, then doesn't this apply to any bridge
> > > > port?
> > >
> > > The main issue here is that pci.txt (and also scheme on github) is
> > > mixing host bridge and root ports into one node. This new property
> > > should be defined at the same place where is supports-clkreq or
> > > reset-gpios, as it belongs to them.
> >
> > Unfortunately that ship has already sailed. So we can split things up,
> > but we still have to allow for the existing cases. I'm happy to take
> > changes splitting up pci-bus.yaml to 2 or 3 schemas (host bridge,
> > root-port, and PCI(e)-PCI(e) bridge?).
>
> Well, no problem. I just need to know how you want to handle backward
> compatibility definitions in YAML. Because it is possible via versioning
> (like in JSONSchema-like structures in OpenAPI versioning) or via

Got a pointer to that?

> deprecated attributes or via defining two schemas (one strict and one
> loose)... There are lot of options and I saw all these options in
> different projects which use YAML or JSON.

The short answer is we don't have a defined way beyond deprecating
properties within a given binding with 'deprecated: true'. The only
versioning we have ATM is the kernel requires a minimum version of
dtschema (which we'll have to bump for all this).

We could have something like:

old-pci-bridge.yaml:
  allOf:
    - $ref: pci-host-bridge.yaml#
    - $ref: pcie-port.yaml#

new-pci-bridge.yaml:
  allOf:
    - $ref: pci-host-bridge.yaml#
  properties:
    pci@0:
      $ref: pcie-port.yaml#

And then both of the above schemas will have $ref to a pci-bridge.yaml
schema which should be most of pci-bus.yaml. linux,pci-domain and
dma-ranges? go to pci-host-bridge.yaml. max-link-speed, num-lanes,
reset-gpios, slot-power-limit-milliwatt, and the pending supply
additions (Broadcom) go to pcie-port.yaml.

> I did not know about github repository, I always looked at schemas and
> definitions only in linux kernel tree and external files which were
> mentioned in kernel tree.
>
> Something I wrote in my RFC email, but I wrote this email patch...
> https://lore.kernel.org/linux-pci/20211023144252.z7ou2l2tvm6cvtf7@pali/

I think we're pretty much in alignment. Look at the Broadcom portdrv
changes proposed if you haven't already. It's all interrelated.

Rob