Re: [PATCH v3 1/3] dt-bindings: Convert graph bindings to json-schema

Laurent Pinchart
2020-11-11T14:00:22Z

Hi Rob and Sameer,

Thank you for the patch.

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.txt b/Documentation/devicetree/bindings/graph.txt
> index 0415e2c53ba0..b7818d61cef7 100644
> --- a/Documentation/devicetree/bindings/graph.txt
> +++ b/Documentation/devicetree/bindings/graph.txt
> @@ -1,128 +1 @@
> -Common bindings for device graphs
> -
> -General concept
> ----------------
> -
> -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.
> -
> -Organisation of ports and endpoints
> ------------------------------------
> -
> -Ports are described by child 'port' nodes contained in the device node.
> -Each port node contains an 'endpoint' subnode for each remote device port
> -connected to this port. If a single port is connected to more than one
> -remote device, an 'endpoint' child node must be provided for each link.
> -If more than one port is present in a device node or there is more than one
> -endpoint at a port, or a port node needs to be associated with a selected
> -hardware interface, a common scheme using '#address-cells', '#size-cells'
> -and 'reg' properties is used to number the nodes.
> -
> -device {
> - ...
> - #address-cells = <1>;
> - #size-cells = <0>;
> -
> - port@0 {
> - #address-cells = <1>;
> - #size-cells = <0>;
> - reg = <0>;
> -
> - endpoint@0 {
> - reg = <0>;
> - ...
> - };
> - endpoint@1 {
> - reg = <1>;
> - ...
> - };
> - };
> -
> - port@1 {
> - reg = <1>;
> -
> - endpoint { ... };
> - };
> -};
> -
> -All 'port' nodes can be grouped under an optional 'ports' node, which
> -allows to specify #address-cells, #size-cells properties for the 'port'
> -nodes independently from any other child device nodes a device might
> -have.
> -
> -device {
> - ...
> - ports {
> - #address-cells = <1>;
> - #size-cells = <0>;
> -
> - port@0 {
> - ...
> - endpoint@0 { ... };
> - endpoint@1 { ... };
> - };
> -
> - port@1 { ... };
> - };
> -};
> -
> -Links between endpoints
> ------------------------
> -
> -Each endpoint should contain a 'remote-endpoint' phandle property that points
> -to the corresponding endpoint in the port of the remote device. In turn, the
> -remote endpoint should contain a 'remote-endpoint' property. If it has one, it
> -must not point to anything other than the local endpoint. Two endpoints with
> -their 'remote-endpoint' phandles pointing at each other form a link between the
> -containing ports.
> -
> -device-1 {
> - port {
> - device_1_output: endpoint {
> - remote-endpoint = <&device_2_input>;
> - };
> - };
> -};
> -
> -device-2 {
> - port {
> - device_2_input: endpoint {
> - remote-endpoint = <&device_1_output>;
> - };
> - };
> -};
> -
> -Required properties
> --------------------
> -
> -If there is more than one 'port' or more than one 'endpoint' node or 'reg'
> -property present in the port and/or endpoint nodes then the following
> -properties are required in a relevant parent node:
> -
> - - #address-cells : number of cells required to define port/endpoint
> - identifier, should be 1.
> - - #size-cells : should be zero.
> -
> -Optional endpoint properties
> -----------------------------
> -
> -- remote-endpoint: phandle to an 'endpoint' subnode of a remote device node.
> -
> +This file has moved to 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 ?

> +
> + ports:
> + type: object
> + description: |
> + If there is more than one port node or 'reg' property present in port
> + nodes then '#address-cells' and '#size-cells' properties are required.
> + In such cases all port nodes can be grouped under 'ports' independently
> + from any other child device nodes a device might have.

Allowing multiple port nodes not grouped in a ports node has created
complexity, with very little gain. Should we forbid that going forward ?

> +
> + properties:
> + "#address-cells":
> + const: 1
> +
> + "#size-cells":
> + const: 0
> +
> + patternProperties:
> + "^port(@[0-9a-f]+)?$":
> + $ref: "#/properties/port"
> + type: object
> +
> + properties:
> + reg:
> + maxItems: 1
> +
> + required:
> + - reg
> +
> +

Maybe a single blank line ?

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> + additionalProperties: false
> +
> +additionalProperties: true
> +
> +examples:
> + # Organisation of ports and endpoints:
> + #
> + # Ports are described by child 'port' nodes contained in the device node.
> + # Each port node contains an 'endpoint' subnode for each remote device port
> + # connected to this port. If a single port is connected to more than one
> + # remote device, an 'endpoint' child node must be provided for each link.
> + # If more than one port is present in a device node or there is more than
> + # one endpoint at a port, or a port node needs to be associated with a
> + # selected hardware interface, a common scheme using '#address-cells',
> + # '#size-cells' and 'reg' properties is used to number the nodes.
> + - |
> + device {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + port@0 {
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <0>;
> +
> + endpoint@0 {
> + reg = <0>;
> + // ...
> + };
> + endpoint@1 {
> + reg = <1>;
> + // ...
> + };
> + };
> +
> + port@1 {
> + reg = <1>;
> +
> + endpoint {
> + // ...
> + };
> + };
> + };
> +
> + # All 'port' nodes can be grouped under an optional 'ports' node, which
> + # allows to specify #address-cells, #size-cells properties for the 'port'
> + # nodes independently from any other child device nodes a device might
> + # have.
> + - |
> + device {
> + // ...
> + ports {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + port@0 {
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <0>;
> + // ...
> +
> + endpoint@0 {
> + reg = <0>;
> + // ...
> + };
> + endpoint@1 {
> + reg = <1>;
> + // ...
> + };
> + };
> +
> + port@1 {
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <1>;
> + // ...
> + };
> + };
> + };
> +
> + # Links between endpoints:
> + #
> + # Each endpoint should contain a 'remote-endpoint' phandle property that
> + # points to the corresponding endpoint in the port of the remote device.
> + # In turn, the remote endpoint should contain a 'remote-endpoint' property.
> + # If it has one, it must not point to anything other than the local endpoint.
> + # Two endpoints with their 'remote-endpoint' phandles pointing at each other
> + # form a link between the containing ports.
> + - |
> + device-1 {
> + port {
> + device_1_output: endpoint {
> + remote-endpoint = <&device_2_input>;
> + };
> + };
> + };
> +
> + device-2 {
> + port {
> + device_2_input: endpoint {
> + remote-endpoint = <&device_1_output>;
> + };
> + };
> + };
> +
> +...

--
Regards,

Laurent Pinchart