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Date:   Wed, 1 Apr 2020 22:25:18 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Rob Herring <robh@kernel.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com>,
        Michal Simek <michal.simek@xilinx.com>,
        devicetree@vger.kernel.org
Subject: Re: [PATCH v6 1/3] dt-bindings: phy: Add DT bindings for Xilinx
 ZynqMP PSGTR PHY
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Hi Rob,

On Fri, Mar 20, 2020 at 10:53:05AM -0600, Rob Herring wrote:
> On Fri, Mar 20, 2020 at 3:50 AM Laurent Pinchart wrote:
> > On Thu, Mar 19, 2020 at 08:35:20PM -0600, Rob Herring wrote:
> > > On Wed, Mar 11, 2020 at 12:32:50PM +0200, Laurent Pinchart wrote:
> > > > From: Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com>
> > > >
> > > > Add DT bindings for the Xilinx ZynqMP PHY. ZynqMP SoCs have a High Speed
> > > > Processing System Gigabit Transceiver which provides PHY capabilities to
> > > > USB, SATA, PCIE, Display Port and Ehernet SGMII controllers.
> > > >
> > > > Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com>
> > > > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > ---
> > > > Changes since v5:
> > > >
> > > > - Document clocks and clock-names properties
> > > > - Document resets and reset-names properties
> > > > - Replace subnodes with an additional entry in the PHY cells
> > > > - Drop lane frequency PHY cell, replaced by reference clock phandle
> > > > - Convert bindings to YAML
> > > > - Reword the subject line
> > > > - Drop Rob's R-b as the bindings have significantly changed
> > > > - Drop resets and reset-names properties
> > > > ---
> > > >  .../bindings/phy/xlnx,zynqmp-psgtr.yaml       | 104 ++++++++++++++++++
> > > >  include/dt-bindings/phy/phy.h                 |   1 +
> > > >  2 files changed, 105 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/phy/xlnx,zynqmp-psgtr.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/phy/xlnx,zynqmp-psgtr.yaml b/Documentation/devicetree/bindings/phy/xlnx,zynqmp-psgtr.yaml
> > > > new file mode 100644
> > > > index 000000000000..9948e4a60e45
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/phy/xlnx,zynqmp-psgtr.yaml
> > > > @@ -0,0 +1,104 @@
> > > > +# SPDX-License-Identifier: GPL-2.0
> > >
> > > For new bindings:
> > >
> > > (GPL-2.0-only OR BSD-2-Clause)
> > >
> > > Though I guess Anurag needs to agree.
> >
> > There's an ongoing similar discussion regarding the DPSUB (DRM/KMS)
> > bindings. Hyun is checking with the Xilinx legal department. If they
> > agree, I'll change the license here, otherwise I'll keep it as-is.
> 
> TBC, the choice is change it or take your toys elsewhere and play by
> yourself. I don't really want to end up with whatever each submitter
> desires. I don't expect there's many companies that object to a
> permissive license.

I don't expect that either, but it's out of my control in any case.
Let's say.

I've heard quite a few times that "the preferred license for new
bindings is GPL-2.0-only OR BSD-2-Clause", but this is the first time I
hear it's a hard requirement. I have missed the decision making process,
I have nothing to question, and I'll spread that message in the future.

> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/phy/xlnx,zynqmp-psgtr.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Xilinx ZynqMP Gigabit Transceiver PHY Device Tree Bindings
> > > > +
> > > > +maintainers:
> > > > +  - Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > +
> > > > +description: |
> > > > +  This binding describes the Xilinx ZynqMP Gigabit Transceiver (GTR) PHY. The
> > > > +  GTR provides four lanes and is used by USB, SATA, PCIE, Display port and
> > > > +  Ethernet SGMII controllers.
> > > > +
> > > > +properties:
> > > > +  "#phy-cells":
> > > > +    const: 4
> > > > +    description: |
> > > > +      The cells contain the following arguments.
> > > > +
> > > > +      - description: The GTR lane
> > > > +        minimum: 0
> > > > +        maximum: 3
> > > > +      - description: The PHY type
> > > > +        enum:
> > > > +          - PHY_TYPE_DP
> > > > +          - PHY_TYPE_PCIE
> > > > +          - PHY_TYPE_SATA
> > > > +          - PHY_TYPE_SGMII
> > > > +          - PHY_TYPE_USB
> > > > +      - description: The PHY instance
> > > > +        minimum: 0
> > > > +        maximum: 1 # for DP, SATA or USB
> > > > +        maximum: 3 # for PCIE or SGMII
> > > > +      - description: The reference clock number
> > > > +        minimum: 0
> > > > +        maximum: 3
> > >
> > > Humm, interesting almost json-schema. I guess it's fine as-is.
> > >
> > > I would like to figure out how to apply a schema like this to the
> > > consumer nodes. We'd have to look up the phandle, get that node's
> > > compatible, find the provider's schema, find #.*-cells property, and
> > > extract a schema from it. Actually, doesn't sound too hard.
> >
> > That would be nice :-)
> >
> > > > +
> > > > +  compatible:
> > > > +    enum:
> > > > +      - xlnx,zynqmp-psgtr-v1.1
> > > > +      - xlnx,zynqmp-psgtr
> > > > +
> > > > +  clocks:
> > > > +    minItems: 1
> > > > +    maxItems: 4
> > > > +    description: |
> > > > +      Clock for each PS_MGTREFCLK[0-3] reference clock input. Unconnected
> > > > +      inputs shall not have an entry.
> > > > +
> > > > +  clock-names:
> > > > +    minItems: 1
> > > > +    maxItems: 4
> > > > +    items:
> > > > +      pattern: "^ref[0-3]$"
> > > > +
> > > > +  reg:
> > > > +    items:
> > > > +      - description: SERDES registers block
> > > > +      - description: SIOU registers block
> > > > +
> > > > +  reg-names:
> > > > +    items:
> > > > +      - const: serdes
> > > > +      - const: siou
> > > > +
> > > > +required:
> > > > +  - "#phy-cells"
> > > > +  - compatible
> > > > +  - reg
> > > > +  - reg-names
> > > > +
> > > > +if:
> > > > +  properties:
> > > > +    compatible:
> > > > +      const: xlnx,zynqmp-psgtr
> > > > +
> > > > +then:
> > > > +  properties:
> > > > +    xlnx,tx-termination-fix:
> > > > +      description: |
> > > > +        Include this for fixing functional issue with the TX termination
> > > > +        resistance in GT, which can be out of spec for the XCZU9EG silicon
> > > > +        version.
> > > > +      type: boolean
> > > > +
> > > > +additionalProperties: false
> > >
> > > This won't work with 'xlnx,tx-termination-fix'. You need to move it to
> > > the main properties section and then do:
> > >
> > > if:
> > >   properties:
> > >     compatible:
> > >       const: xlnx,zynqmp-psgtr-v1.1
> >
> > It doesn't make a big difference as only two compatible values are
> > allowed, but is there a way to express the condition the other way
> > around, if (compatible != "xlnx,zynqmp-psgtr") ?
> 
> if:
>   properties:
>     compatible:
>       not:
>         const: xlnx,zynqmp-psgtr
> 
> I think if: { not: ... } would also work. You'll have to test them out.

I tried both, and neither worked. No big deal, I'll keep the current
expression.

> > > then:
> > >   properties:
> > >     xlnx,tx-termination-fix: false
> >
> > This works.
> >
> > > I think this would also work:
> > >
> > >   not:
> > >     required:
> > >       - xlnx,tx-termination-fix
> >
> > I've tested it and it works, but I'm not sure why, given that the
> > property isn't required required in the first place. Could you enlighten
> > me ?
> 
> 'required' is true or false based on presence or absence of properties
> in the list. If 'xlnx,tx-termination-fix' is present, then 'required'
> evaluates to true. And the inverse is true. Then we take the inverse
> of of that with 'not'.
> 
> The first case is what trips me up more because a property not present
> evaluates to true. So if you look at 'select' schemas, we have to make
> any properties we list (compatible typically) required.

-- 
Regards,

Laurent Pinchart