Date:   Mon, 12 Oct 2020 07:19:43 +0000
From:   <Eugen.Hristev@...rochip.com>
To:     <laurent.pinchart@...asonboard.com>
CC:     <robh+dt@...nel.org>, <sakari.ailus@....fi>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 1/3] dt-bindings: media: atmel: csi2dc: add bindings
 for microchip csi2dc

On 11.10.2020 00:17, Laurent Pinchart wrote:
> Hi Eugen,
> 
> Thank you for the patch.

Hi,

Thank you for your review,

> 
> On Wed, Aug 26, 2020 at 09:51:40AM +0300, Eugen Hristev wrote:
>> Add bindings documentation for Microchip CSI2 Demultiplexer controller.
>>
>> CSI2DC is a demultiplexer from Synopsys IDI interface specification to
>> parallel interface connection or direct memory access.
>>
>> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
>> ---
>> Changes in v3:
>> - Removed some text from description, as it was explained in the schema
>> - fixed other things as per Rob's review
>> - moved some text inside the schema, like the clock description
>>
>> Changes in v2:
>> - fixed warnings reported by dt_binding_check
>>
>>   .../bindings/media/microchip,csi2dc.yaml      | 174 ++++++++++++++++++
>>   1 file changed, 174 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/media/microchip,csi2dc.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/media/microchip,csi2dc.yaml b/Documentation/devicetree/bindings/media/microchip,csi2dc.yaml
>> new file mode 100644
>> index 000000000000..b4c1b8800a3b
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/media/microchip,csi2dc.yaml
>> @@ -0,0 +1,174 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/media/microchip,csi2dc.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Microchip CSI2 Demux Controller (CSI2DC)
>> +
>> +maintainers:
>> +  - Eugen Hristev <eugen.hristev@...rochip.com>
>> +
>> +description:
>> +  CSI2DC - Camera Serial Interface 2 Demux Controller
>> +
>> +  CSI2DC is a hardware block that receives incoming data from an IDI interface
>> +  and filters packets based on their data type and virtual channel identifier,
>> +  then converts the byte stream into a cross clock domain to a pixel stream
>> +  to a parallel interface that can be read by a sensor controller.
>> +
>> +  CSI2DC provides two pipes, one video pipe and one data pipe. Video pipe
>> +  is connected to a sensor controller and the data pipe is accessible
>> +  as a DMA slave port to a DMA controller.
>> +
>> +  CSI2DC supports a single 'port' node as a source pad with Synopsys 32-bit
>> +  IDI interface. The connected endpoint must be a IDI interface compatible
>> +  device (like Synopsys CSI2HOST) , that can provide 32-bit IDI interface
>> +  connection as sink pad.
>> +  For media entity and endpoints please refer to the bindings defined in
>> +  Documentation/devicetree/bindings/media/video-interfaces.txt.
>> +  For Synopsys IDI interface please refer to
>> +  Documentation/devicetree/bindings/media/snps,dw-csi-plat.txt
>> +
>> +  CSI2DC supports one 'port' node as sink pad with parallel interface. This is
>> +  called video pipe.
>> +  This port has an 'endpoint' can then be used as a source pad for another
>> +  controller (next in pipeline).
>> +  Please refer to the bindings defined in
>> +  Documentation/devicetree/bindings/media/video-interfaces.txt.
>> +
>> +  CSI2DC also supports direct access to the data through AHB, via DMA channel,
>> +  called data pipe.
>> +  Because of this, the sink 'port' child node (second) is not mandatory.
>> +  If the sink 'port' child node is missing, only data pipe is available.
>> +
>> +properties:
>> +  compatible:
>> +    const: microchip,sama7g5-csi2dc
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  clocks:
>> +    maxItems: 2
>> +
>> +  clock-names:
>> +    description:
>> +      CSI2DC must have two clocks to function correctly. One clock is the
>> +      peripheral clock for the inside functionality of the hardware block.
>> +      This is named 'pclk'. The second clock must be the cross domain clock,
>> +      in which CSI2DC will perform clock crossing. This clock must be fed
>> +      by the next controller in pipeline, which usually is a sensor controller.
>> +      Normally this clock should be given by this sensor controller who
>> +      is also a clock source. This clock is named 'scck', sensor controller clock.
>> +    items:
>> +      - const: pclk
>> +      - const: scck
>> +
>> +  microchip,clk-gated:
>> +    type: boolean
>> +    description:
>> +      If present, indicates that the clock is gated.
>> +      Otherwise, the clock is free-running.
> 
> I don't think this belongs to the DT bindings, it should instead be
> queried from the source subdev at runtime.

If this should be queried, do you know what is the v4l2 mechanism to 
query such information ?
The subdevice is connected through a port interface to this device, so 
it was natural for me to fully describe the interface in the devicetree 
port description

> 
>> +
>> +  microchip,inter-line-delay:
>> +    allOf:
>> +    - $ref: /schemas/types.yaml#/definitions/uint32
>> +    - minimum: 1
>> +    - maximum: 16
>> +    default: 16
>> +    description:
>> +      Indicates how many clock cycles should be introduced between each line.
> 
> This also sounds like a configuration parameter. How does one compute
> the right value for this ?

I think this is a delay that can be added inside the hardware block, 
depending on the interface speed and bandwidth. I will try to understand 
more details from the hardware design and come back with a more detailed 
answer.

> 
>> +
>> +  port@0:
>> +    type: object
>> +    description:
>> +      Input port node, single endpoint describing the input pad.
>> +
>> +    properties:
>> +      reg:
>> +        const: 0
>> +
>> +      endpoint:
>> +        type: object
>> +
>> +        properties:
>> +          remote-endpoint: true
>> +
>> +        required:
>> +          - remote-endpoint
>> +
>> +        additionalProperties: false
>> +
>> +    additionalProperties: false
>> +
>> +  port@1:
>> +    type: object
>> +    description:
>> +      Output port node, single endpoint, describing the output pad.
>> +
>> +    properties:
>> +      '#address-cells':
>> +        const: 1
>> +
>> +      '#size-cells':
>> +        const: 0
>> +
>> +      reg:
>> +        const: 1
>> +
>> +    patternProperties:
>> +      "^endpoint@[0-3]$":
>> +        type: object
>> +
>> +        properties:
>> +          reg:
>> +            enum: [0, 1, 2, 3]
>> +            description: virtual channel for the endpoint
> 
> The virtual channel used by the source is also something that needs to
> be queried from the source at runtime, it doesn't belong to this
> binding.

The same question as for the gated clock configuration. How can we use 
v4l2 subdevice API to obtain such information from the subdevice? And if 
the subdevice does not offer such information ?

Thanks again,

Eugen
> 
>> +
>> +          remote-endpoint: true
>> +
>> +        required:
>> +          - remote-endpoint
>> +          - reg
>> +
>> +        additionalProperties: false
>> +
>> +    additionalProperties: false
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - clocks
>> +  - clock-names
>> +  - port@0
>> +
>> +examples:
>> +  - |
>> +    csi2dc@...04000 {
>> +        compatible = "microchip,sama7g5-csi2dc";
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +        reg = <0xe1404000 0x500>;
>> +        clocks = <&pclk>, <&scck>;
>> +        clock-names = "pclk", "scck";
>> +
>> +        port@0 {
>> +               reg = <0>; /* must be 0, first child port */
>> +               csi2dc_in: endpoint { /* input from IDI interface */
>> +                     remote-endpoint = <&csi2host_out>;
>> +               };
>> +        };
>> +
>> +        port@1 {
>> +                #address-cells = <1>;
>> +                #size-cells = <0>;
>> +                reg = <1>; /* must be 1, second child port */
>> +                csi2dc_out: endpoint@2 {
>> +                        reg = <2>;  /* virtual channel identifier */
>> +                        remote-endpoint = <&xisc_in>; /* output to sensor controller */
>> +                };
>> +        };
>> +    };
>> +
>> +...
> 
> --
> Regards,
> 
> Laurent Pinchart
> 

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