Re: [PATCH v3 2/4] dt-bindings: media: add Maxim MAX96714F GMSL2 Deserializer

[Julien Massot <julien.massot@collabora.com>]

Hi Sakari,

Thanks for the review!

On 2/9/24 10:48, Sakari Ailus wrote:
> Hi Julien,
> 
> On Thu, Jan 11, 2024 at 02:03:47PM +0100, Julien Massot wrote:
>> Add DT bindings for Maxim MAX96714F GMSL2 Deserializer.
>>
>> Signed-off-by: Julien Massot <julien.massot@collabora.com>
>>
>> ---
>> Change since v2:
>>   - remove reg description
>>   - rename enable gpio to powerdown
>>   - use generic node name: i2c, serializer, deserializer
>> ---
>>   .../bindings/media/i2c/maxim,max96714f.yaml   | 171 ++++++++++++++++++
>>   1 file changed, 171 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/media/i2c/maxim,max96714f.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/media/i2c/maxim,max96714f.yaml b/Documentation/devicetree/bindings/media/i2c/maxim,max96714f.yaml
>> new file mode 100644
>> index 000000000000..2423d166c954
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/media/i2c/maxim,max96714f.yaml
>> @@ -0,0 +1,171 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +# Copyright (C) 2024 Collabora Ltd.
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/media/i2c/maxim,max96714f.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Maxim MAX96714 GMSL2 to CSI-2 Deserializer
>> +
>> +maintainers:
>> +  - Julien Massot <julien.massot@collabora.com>
>> +
>> +description: |
>> +  The MAX96714F deserializer converts GMSL2 serial inputs into MIPI
>> +  CSI-2 D-PHY or C-PHY formatted output. The device allows the GMSL2 link to

Description is wrong if the MAX96717F is supporting C-PHY MAX96714F doesn't.
I will remove the mention to C-PHY sorry for the confusion.

>> +  simultaneously transmit bidirectional control-channel data while forward
>> +  video transmissions are in progress. The MAX96714F can connect to one
>> +  remotely located serializer using industry-standard coax or STP
>> +  interconnects. The device cans operate in pixel or tunnel mode. In pixel mode
>> +  the MAX96714F can select individual video stream, while the tunnel mode forward all
>> +  the MIPI data received by the serializer.
>> +
>> +  The GMSL2 serial link operates at a fixed rate of 3Gbps in the
>> +  forward direction and 187.5Mbps in the reverse direction.
>> +
>> +properties:
>> +  compatible:
>> +    const: maxim,max96714f
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  powerdown-gpios:
>> +    maxItems: 1
>> +    description:
>> +      Specifier for the GPIO connected to the PWDNB pin.
>> +
>> +  ports:
>> +    $ref: /schemas/graph.yaml#/properties/ports
>> +
>> +    properties:
>> +      port@0:
>> +        $ref: /schemas/graph.yaml#/properties/port
>> +        unevaluatedProperties: false
>> +        description: GMSL Input
>> +        properties:
>> +          endpoint:
>> +            $ref: /schemas/media/video-interfaces.yaml#
>> +            unevaluatedProperties: false
>> +            description:
>> +              Endpoint for GMSL2-Link port.
>> +
>> +      port@1:
>> +        $ref: /schemas/graph.yaml#/$defs/port-base
>> +        unevaluatedProperties: false
>> +        description: CSI-2 Output port
>> +
>> +        properties:
>> +          endpoint:
>> +            $ref: /schemas/media/video-interfaces.yaml#
>> +            unevaluatedProperties: false
>> +
>> +            properties:
>> +              data-lanes:
>> +                minItems: 1
>> +                maxItems: 4
>> +
>> +              link-frequencies:
>> +                maxItems: 1
>> +
>> +              bus-type:
>> +                enum:
>> +                  - 4 # MEDIA_BUS_TYPE_CSI2_DPHY
> 
> MEDIA_BUS_TYPE_CSI2_CPHY (1) is missing. Even if the driver doesn't support
> it, it would be best to list it here.

After verification the hardware only support D-PHY and not C-PHY, will
drop the required
property for 'bus-type'.

> 
>> +
>> +            required:
>> +              - data-lanes
>> +              - bus-type
>> +
>> +    required:
>> +      - port@1
> 
> Why port@1 but not port@0?

The device can be used as a pattern generator, so this is fine not to
have a serializer connected to the port@0, but it makes no sense to 
leave the deserializer CSI port not connected.

> 
>> +
>> +  i2c-gate:
>> +    $ref: /schemas/i2c/i2c-controller.yaml
>> +    unevaluatedProperties: false
>> +    description: |
>> +      The MAX96714 will pass through and forward the I2C requests from the
>> +      incoming I2C bus over the GMSL2 link. Therefore it supports an i2c-gate
>> +      subnode to configure a serializer.
>> +
>> +  port0-poc-supply:
>> +    description: Regulator providing Power over Coax for the GMSL port
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - ports
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/gpio/gpio.h>
>> +    #include <dt-bindings/media/video-interfaces.h>
>> +
>> +    i2c {
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +
>> +        deserializer@28 {
>> +            compatible = "maxim,max96714f";
>> +            reg = <0x28>;
>> +            powerdown-gpios = <&main_gpio0 37 GPIO_ACTIVE_LOW>;
>> +
>> +            ports {
>> +                #address-cells = <1>;
>> +                #size-cells = <0>;
>> +                port@0 {
>> +                    reg = <0>;
>> +                    max96714_gmsl_in: endpoint {
>> +                        remote-endpoint = <&max96917f_gmsl_out>;
>> +                    };
>> +                };
>> +
>> +                port@1 {
>> +                    reg = <1>;
>> +                    max96714_csi_out: endpoint {
>> +                        bus-type = <MEDIA_BUS_TYPE_CSI2_DPHY>;
>> +                        clock-lanes = <0>;
> 
> clock-lanes isn't listed in bindings. You can drop it from here.
Ok

> 
>> +                        data-lanes = <1 2 3 4>;
>> +                        link-frequencies = /bits/ 64 <400000000>;
>> +                        remote-endpoint = <&csi_in>;
>> +                    };
>> +                };
>> +            };
>> +
>> +            i2c-gate {
>> +                #address-cells = <1>;
>> +                #size-cells = <0>;
>> +
>> +                serializer@40 {
>> +                    compatible = "maxim,max96717f";
>> +                    reg = <0x40>;
>> +                    gpio-controller;
>> +                    #gpio-cells = <2>;
>> +                    #clock-cells = <0>;
>> +
>> +                    ports {
>> +                        #address-cells = <1>;
>> +                        #size-cells = <0>;
>> +
>> +                        port@0 {
>> +                            reg = <0>;
>> +                            max96717f_csi_in: endpoint {
>> +                                data-lanes = <1 2>;
>> +                                lane-polarities = <1 0 1>;
> 
> Shouldn't lane-polarities be mentioned in bindings, too?

You are right I will add lane-polarities to my next patchset.
> 
>> +                                remote-endpoint = <&sensor_out>;
>> +                            };
>> +                        };
>> +
>> +                        port@1 {
>> +                            reg = <1>;
>> +                            max96917f_gmsl_out: endpoint {
>> +                                remote-endpoint = <&max96714_gmsl_in>;
>> +                            };
>> +                        };
>> +                    };
>> +                };
>> +            };
>> +        };
>> +    };
>> +...
> 

Best regards,

-- 
Julien Massot
Senior Software Engineer
Collabora Ltd.
Platinum Building, St John's Innovation Park, Cambridge CB4 0DS, UK
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