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Date:   Thu, 12 Nov 2020 09:56:19 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Rob Herring <robh@kernel.org>
Cc:     devicetree@vger.kernel.org, Sameer Pujar <spujar@nvidia.com>,
        Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        Jacopo Mondi <jacopo+renesas@jmondi.org>
Subject: Re: [PATCH v3 1/3] dt-bindings: Convert graph bindings to json-schema
Message-ID: <20201112075619.GA7931@pendragon.ideasonboard.com>
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Hi Rob,

On Wed, Nov 11, 2020 at 05:03:26PM -0600, Rob Herring wrote:
> On Wed, Nov 11, 2020 at 8:27 AM Laurent Pinchart wrote:
> > On Wed, Nov 11, 2020 at 08:25:40AM -0600, Rob Herring wrote:
> > > On Wed, Nov 11, 2020 at 8:00 AM Laurent Pinchart wrote:
> > > > On Mon, Nov 02, 2020 at 02:36:54PM -0600, Rob Herring wrote:
> > > > > From: Sameer Pujar <spujar@nvidia.com>
> > > > >
> > > > > Convert device tree bindings of graph to YAML format. Currently graph.txt
> > > > > doc is referenced in multiple files and all of these need to use schema
> > > > > references. For now graph.txt is updated to refer to graph.yaml.
> > > > >
> > > > > For users of the graph binding, they should reference to the graph
> > > > > schema from either 'ports' or 'port' property:
> > > > >
> > > > > properties:
> > > > >   ports:
> > > > >     type: object
> > > > >     $ref: graph.yaml#/properties/ports
> > > > >
> > > > >     properties:
> > > > >       port@0:
> > > > >         description: What data this port has
> > > > >
> > > > >       ...
> > > > >
> > > > > Or:
> > > > >
> > > > > properties:
> > > > >   port:
> > > > >     description: What data this port has
> > > > >     type: object
> > > > >     $ref: graph.yaml#/properties/port
> > > >
> > > > Sounds like a good approach.
> > > >
> > > > > Signed-off-by: Sameer Pujar <spujar@nvidia.com>
> > > > > Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
> > > > > Signed-off-by: Rob Herring <robh@kernel.org>
> > > > > ---
> > > > > v3:
> > > > >  - Move port 'reg' to port@* and make required
> > > > >  - Make remote-endpoint required
> > > > >  - Add 'additionalProperties: true' now required
> > > > >  - Fix yamllint warnings
> > > > >
> > > > >  Documentation/devicetree/bindings/graph.txt  | 129 +-----------
> > > > >  Documentation/devicetree/bindings/graph.yaml | 199 +++++++++++++++++++
> > > > >  2 files changed, 200 insertions(+), 128 deletions(-)
> > > > >  create mode 100644 Documentation/devicetree/bindings/graph.yaml
> > >
> > > [...]
> > >
> > > > > diff --git a/Documentation/devicetree/bindings/graph.yaml b/Documentation/devicetree/bindings/graph.yaml
> > > > > new file mode 100644
> > > > > index 000000000000..b56720c5a13e
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/graph.yaml
> > > > > @@ -0,0 +1,199 @@
> > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +$id: http://devicetree.org/schemas/graph.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: Common bindings for device graphs
> > > > > +
> > > > > +description: |
> > > > > +  The hierarchical organisation of the device tree is well suited to describe
> > > > > +  control flow to devices, but there can be more complex connections between
> > > > > +  devices that work together to form a logical compound device, following an
> > > > > +  arbitrarily complex graph.
> > > > > +  There already is a simple directed graph between devices tree nodes using
> > > > > +  phandle properties pointing to other nodes to describe connections that
> > > > > +  can not be inferred from device tree parent-child relationships. The device
> > > > > +  tree graph bindings described herein abstract more complex devices that can
> > > > > +  have multiple specifiable ports, each of which can be linked to one or more
> > > > > +  ports of other devices.
> > > > > +
> > > > > +  These common bindings do not contain any information about the direction or
> > > > > +  type of the connections, they just map their existence. Specific properties
> > > > > +  may be described by specialized bindings depending on the type of connection.
> > > > > +
> > > > > +  To see how this binding applies to video pipelines, for example, see
> > > > > +  Documentation/devicetree/bindings/media/video-interfaces.txt.
> > > > > +  Here the ports describe data interfaces, and the links between them are
> > > > > +  the connecting data buses. A single port with multiple connections can
> > > > > +  correspond to multiple devices being connected to the same physical bus.
> > > > > +
> > > > > +maintainers:
> > > > > +  - Philipp Zabel <p.zabel@pengutronix.de>
> > > > > +
> > > > > +select: false
> > > > > +
> > > > > +properties:
> > > > > +  port:
> > > > > +    type: object
> > > > > +    description:
> > > > > +      If there is more than one endpoint node or 'reg' property present in
> > > > > +      endpoint nodes then '#address-cells' and '#size-cells' properties are
> > > > > +      required.
> > > > > +
> > > > > +    properties:
> > > > > +      "#address-cells":
> > > > > +        const: 1
> > > > > +
> > > > > +      "#size-cells":
> > > > > +        const: 0
> > > > > +
> > > > > +    patternProperties:
> > > > > +      "^endpoint(@[0-9a-f]+)?$":
> > > > > +        type: object
> > > > > +        properties:
> > > > > +          reg:
> > > > > +            maxItems: 1
> > > > > +
> > > > > +          remote-endpoint:
> > > > > +            description: |
> > > > > +              phandle to an 'endpoint' subnode of a remote device node.
> > > > > +            $ref: /schemas/types.yaml#/definitions/phandle
> > > > > +
> > > > > +        required:
> > > > > +          - remote-endpoint
> > > >
> > > > As noted elsewhere, this shouldn't be required.
> > > >
> > > > Should we set additionalProperties: false here ?
> > >
> > > No, we've got a bunch of properties that get added to endpoint nodes.
> > > There's a few cases where 'port' nodes have properties too.
> >
> > I meant the port node, which I wasn't aware needed additional
> > properties. Do you have any example ? (I wonder if you will point me to
> > bindings that I have written ;-))
> 
> Not you, but Renesas. dual-lvds-{odd,even}-pixels was the only one I
> think. But really, I think we could actually drop those if the port
> numbering defines even/odd instead. There's a patch I just reviewed
> for common dual lane panels. See
> 1604993797-14240-1-git-send-email-victor.liu@nxp.com

We've discussed this before, see

Subject: Re: [PATCH v2 7/9] drm: rcar-du: lvds: Add dual-LVDS panels support
Message-ID: <20190815130834.GM5011@pendragon.ideasonboard.com>

"But what will then happen if you panel has more than two ports (for
audio for instance, or for other types of video links) ? It may not be
possible to always use port 0 and 1 for the LVDS even and odd pixels in
DT bindings of a particular panel or bridge."

-- 
Regards,

Laurent Pinchart