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Message-ID: <CAL_JsqKx+JEpROza5+M42Bj+CkL=2V9dYkva4bubXBweVseLpw@mail.gmail.com>
Date: Mon, 15 Mar 2021 10:59:33 -0600
From: Rob Herring <robh@...nel.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>,
devicetree@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [PATCH] dt-bindings: media: Convert video-mux to DT schema
On Fri, Mar 12, 2021 at 2:48 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Rob,
>
> On Fri, Mar 12, 2021 at 08:33:06AM -0700, Rob Herring wrote:
> > On Fri, Mar 12, 2021 at 3:06 AM Laurent Pinchart wrote:
> > > On Fri, Mar 12, 2021 at 09:29:04AM +0200, Sakari Ailus wrote:
> > > > On Fri, Mar 12, 2021 at 03:25:11AM +0200, Laurent Pinchart wrote:
> > > > > On Thu, Mar 11, 2021 at 04:40:42PM -0700, Rob Herring wrote:
> > > > > > Now that we have the graph schema, convert the video-mux binding to DT
> > > > > > schema.
> > > > > >
> > > > > > Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > > > > > Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > > > > > Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> > > > > > Cc: linux-media@...r.kernel.org
> > > > > > Signed-off-by: Rob Herring <robh@...nel.org>
> > > > > > ---
> > > > > > .../devicetree/bindings/media/video-mux.txt | 60 ------------
> > > > > > .../devicetree/bindings/media/video-mux.yaml | 93 +++++++++++++++++++
> > > > > > 2 files changed, 93 insertions(+), 60 deletions(-)
> > > > > > delete mode 100644 Documentation/devicetree/bindings/media/video-mux.txt
> > > > > > create mode 100644 Documentation/devicetree/bindings/media/video-mux.yaml
> > > > > >
> > > > > > diff --git a/Documentation/devicetree/bindings/media/video-mux.txt b/Documentation/devicetree/bindings/media/video-mux.txt
> > > > > > deleted file mode 100644
> > > > > > index 63b9dc913e45..000000000000
> > > > > > --- a/Documentation/devicetree/bindings/media/video-mux.txt
> > > > > > +++ /dev/null
> > > > > > @@ -1,60 +0,0 @@
> > > > > > -Video Multiplexer
> > > > > > -=================
> > > > > > -
> > > > > > -Video multiplexers allow to select between multiple input ports. Video received
> > > > > > -on the active input port is passed through to the output port. Muxes described
> > > > > > -by this binding are controlled by a multiplexer controller that is described by
> > > > > > -the bindings in Documentation/devicetree/bindings/mux/mux-controller.txt
> > > > > > -
> > > > > > -Required properties:
> > > > > > -- compatible : should be "video-mux"
> > > > > > -- mux-controls : mux controller node to use for operating the mux
> > > > > > -- #address-cells: should be <1>
> > > > > > -- #size-cells: should be <0>
> > > > > > -- port@*: at least three port nodes containing endpoints connecting to the
> > > > > > - source and sink devices according to of_graph bindings. The last port is
> > > > > > - the output port, all others are inputs.
> > > > > > -
> > > > > > -Optionally, #address-cells, #size-cells, and port nodes can be grouped under a
> > > > > > -ports node as described in Documentation/devicetree/bindings/graph.txt.
> > > > > > -
> > > > > > -Example:
> > > > > > -
> > > > > > - mux: mux-controller {
> > > > > > - compatible = "gpio-mux";
> > > > > > - #mux-control-cells = <0>;
> > > > > > -
> > > > > > - mux-gpios = <&gpio1 15 GPIO_ACTIVE_HIGH>;
> > > > > > - };
> > > > > > -
> > > > > > - video-mux {
> > > > > > - compatible = "video-mux";
> > > > > > - mux-controls = <&mux>;
> > > > > > - #address-cells = <1>;
> > > > > > - #size-cells = <0>;
> > > > > > -
> > > > > > - port@0 {
> > > > > > - reg = <0>;
> > > > > > -
> > > > > > - mux_in0: endpoint {
> > > > > > - remote-endpoint = <&video_source0_out>;
> > > > > > - };
> > > > > > - };
> > > > > > -
> > > > > > - port@1 {
> > > > > > - reg = <1>;
> > > > > > -
> > > > > > - mux_in1: endpoint {
> > > > > > - remote-endpoint = <&video_source1_out>;
> > > > > > - };
> > > > > > - };
> > > > > > -
> > > > > > - port@2 {
> > > > > > - reg = <2>;
> > > > > > -
> > > > > > - mux_out: endpoint {
> > > > > > - remote-endpoint = <&capture_interface_in>;
> > > > > > - };
> > > > > > - };
> > > > > > - };
> > > > > > -};
> > > > > > diff --git a/Documentation/devicetree/bindings/media/video-mux.yaml b/Documentation/devicetree/bindings/media/video-mux.yaml
> > > > > > new file mode 100644
> > > > > > index 000000000000..780fbbd46a38
> > > > > > --- /dev/null
> > > > > > +++ b/Documentation/devicetree/bindings/media/video-mux.yaml
> > > > > > @@ -0,0 +1,93 @@
> > > > > > +# SPDX-License-Identifier: GPL-2.0
> > > > > > +%YAML 1.2
> > > > > > +---
> > > > > > +$id: http://devicetree.org/schemas/media/video-mux.yaml#
> > > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > > +
> > > > > > +title: Video Multiplexer
> > > > > > +
> > > > > > +maintainers:
> > > > > > + - Sakari Ailus <sakari.ailus@...ux.intel.com>
> > > > > > + - Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > > > > > +
> > > > > > +description:
> > > > > > + Video multiplexers allow to select between multiple input ports. Video
> > > > > > + received on the active input port is passed through to the output port. Muxes
> > > > > > + described by this binding are controlled by a multiplexer controller.
> > > > > > +
> > > > > > +properties:
> > > > > > + compatible:
> > > > > > + const: video-mux
> > > > > > +
> > > > > > + mux-controls:
> > > > > > + maxItems: 1
> > > > > > +
> > > > > > + '#address-cells':
> > > > > > + const: 1
> > > > > > +
> > > > > > + '#size-cells':
> > > > > > + const: 0
> > > > > > +
> > > > > > + ports:
> > > > > > + $ref: /schemas/graph.yaml#/properties/ports
> > > > > > +
> > > > > > + patternProperties:
> > > > > > + '^port@':
> > > > > > + $ref: /schemas/graph.yaml#/properties/port
> > > > >
> > > > > Should we require at least port@0, port@1 and port@2 ?
> > > > >
> > > > > > +
> > > > > > +patternProperties:
> > > > > > + '^port@':
> > > > > > + $ref: /schemas/graph.yaml#/properties/port
> > > > > > + description:
> > > > > > + At least three port nodes containing endpoints connecting to the source
> > > > > > + and sink devices according to of_graph bindings. The last port is the
> > > > > > + output port, all others are inputs.
> > > > > > +
> > > > > > +required:
> > > > > > + - compatible
> > > > > > + - mux-controls
> > > > >
> > > > > Should a constraint be added to ensure that either a ports node or
> > > > > port@0, port@1 and port@2 nodes exists ?
> > > >
> > > > It's not meaningful to have this device without such nodes. But a mux with
> > > > more ports could be connected in a way that leaves one or both of ports 1
> > > > and 2 unconnected. It's still not a likely configuration but a possible
> > > > one.
> > >
> > > Those ports wouldn't be connected, but they could still exist in DT.
> >
> > Could or must? I think we could have both cases. If there's never a
> > connection on a board no point in having the node there. If there's a
> > possible connection (via a connector and overlay), then we may want
> > the node.
>
> I tend to treat ports as mandatory and endpoints as optional, as the
> former describe a intrinsic property of the device and the latter a
> connection in a specific system.
>
> Looking at the video-mux driver, it first finds the number of the last
> port, and then creates N V4L2 subdev pads, regardless of whether a port
> exists for it. There's thus an implicit assumption that ports will be
> numbered 0 to N-1 and will all exist. If a port doesn't exist in DT, the
> driver should still operate correctly as far as I can tell, but it will
> in any case create N pads.
>
> Now, that's a driver implementation, but given that the bindings are for
> a generic mux device, the driver matters here. I'd be fine making ports
> optional and modifying the driver, or making them mandatory in DT, but I
> think it's important to at least synchronize the bindings and the
> driver.
I guess we can always loosen the constraints if the need arises, so
I've made the port nodes required and applied:
diff --git a/Documentation/devicetree/bindings/media/video-mux.yaml
b/Documentation/devicetree/bindings/media/video-mux.yaml
index 780fbbd46a38..2f28a7dad93f 100644
--- a/Documentation/devicetree/bindings/media/video-mux.yaml
+++ b/Documentation/devicetree/bindings/media/video-mux.yaml
@@ -35,6 +35,11 @@ properties:
'^port@':
$ref: /schemas/graph.yaml#/properties/port
+ required:
+ - port@0
+ - port@1
+ - port@2
+
patternProperties:
'^port@':
$ref: /schemas/graph.yaml#/properties/port
@@ -47,6 +52,14 @@ required:
- compatible
- mux-controls
+oneOf:
+ - required:
+ - ports
+ - required:
+ - port@0
+ - port@1
+ - port@2
+
additionalProperties: false
examples:
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