linux-kernel - Re: [PATCH v2 2/4] dt-bindings: display: bridge: add it66121 bindings

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Date:   Fri, 13 Mar 2020 15:12:13 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Phong LE <ple@...libre.com>
Cc:     airlied@...ux.ie, daniel@...ll.ch, robh+dt@...nel.org,
        mark.rutland@....com, a.hajda@...sung.com, jonas@...boo.se,
        jernej.skrabec@...l.net, sam@...nborg.org, mripard@...nel.org,
        heiko.stuebner@...obroma-systems.com, linus.walleij@...aro.org,
        stephan@...hold.net, icenowy@...c.io, broonie@...nel.org,
        mchehab+samsung@...nel.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, Jonathan.Cameron@...wei.com,
        andriy.shevchenko@...ux.intel.com, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dt-bindings: display: bridge: add it66121 bindings

On 13/03/2020 14:40, Laurent Pinchart wrote:
> Hi Phong,
> 
> Thank you for the patch.
> 
> On Wed, Mar 11, 2020 at 01:51:33PM +0100, Phong LE wrote:
>> Add the ITE bridge HDMI it66121 bindings.
>>
>> Signed-off-by: Phong LE <ple@...libre.com>
>> ---
>>  .../bindings/display/bridge/ite,it66121.yaml  | 98 +++++++++++++++++++
>>  1 file changed, 98 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/display/bridge/ite,it66121.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/display/bridge/ite,it66121.yaml b/Documentation/devicetree/bindings/display/bridge/ite,it66121.yaml
>> new file mode 100644
>> index 000000000000..1717e880d130
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/display/bridge/ite,it66121.yaml
>> @@ -0,0 +1,98 @@
>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/display/bridge/ite,it66121.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: ITE it66121 HDMI bridge Device Tree Bindings
>> +
>> +maintainers:
>> +  - Phong LE <ple@...libre.com>
>> +  - Neil Armstrong <narmstrong@...libre.com>
>> +
>> +description: |
>> +  The IT66121 is a high-performance and low-power single channel HDMI
>> +  transmitter, fully compliant with HDMI 1.3a, HDCP 1.2 and backward compatible
>> +  to DVI 1.0 specifications.
>> +
>> +properties:
>> +  compatible:
>> +    const: ite,it66121
>> +
>> +  reg:
>> +    maxItems: 1
>> +    description: base I2C address of the device
>> +
>> +  reset-gpios:
>> +    maxItems: 1
>> +    description: GPIO connected to active low reset
>> +
>> +  vrf12-supply:
>> +    maxItems: 1
>> +    description: Regulator for 1.2V analog core power.
>> +
>> +  vcn33-supply:
>> +    maxItems: 1
>> +    description: Regulator for 3.3V digital core power.
>> +
>> +  vcn18-supply:
>> +    maxItems: 1
>> +    description: Regulator for 1.8V IO core power.
>> +
>> +  interrupts:
>> +    maxItems: 1
>> +
>> +  pclk-dual-edge:
>> +    maxItems: 1
>> +    description: enable pclk dual edge mode.
> 
> I'm having a bit of trouble understanding how this operates. Looking at
> the driver code the property is only taken into account to calculate the
> maximum allowed frequency. How is the IT66121 configured for single vs.
> dual pixel clock edge mode ?


Dual edge mode is Dual-Data-Rate mode, the normal mode is MEDIA_BUS_FMT_RGB888_1X24 and dual edge is
MEDIA_BUS_FMT_RGB888_2X12_LE (or MEDIA_BUS_FMT_RGB888_2X12_BE, not sure) on a single clock period.

This should be negociated at runtime, but the bus width should be specified somewhere to select
one of the modes.

Neil

> 
>> +
>> +  port:
>> +    type: object
>> +
>> +    properties:
>> +      endpoint:
>> +        type: object
>> +        description: |
>> +          Input endpoints of the bridge.
>> +
>> +    required:
>> +      - endpoint
> 
> You should have two ports, one for the bridge input, and one for the
> bridge output.
> 
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - reset-gpios
>> +  - vrf12-supply
>> +  - vcn33-supply
>> +  - vcn18-supply
>> +  - interrupts
>> +  - port
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    i2c6 {
>> +      #address-cells = <1>;
>> +      #size-cells = <0>;
>> +
>> +      it66121hdmitx: it66121hdmitx@4c {
>> +        compatible = "ite,it66121";
>> +        pinctrl-names = "default";
>> +        pinctrl-0 = <&ite_pins_default>;
>> +        vcn33-supply = <&mt6358_vcn33_wifi_reg>;
>> +        vcn18-supply = <&mt6358_vcn18_reg>;
>> +        vrf12-supply = <&mt6358_vrf12_reg>;
>> +        reset-gpios = <&pio 160 1 /* GPIO_ACTIVE_LOW */>;
>> +        interrupt-parent = <&pio>;
>> +        interrupts = <4 8 /* IRQ_TYPE_LEVEL_LOW */>;
>> +        reg = <0x4c>;
>> +        pclk-dual-edge;
>> +
>> +        port {
>> +          it66121_in: endpoint {
>> +            remote-endpoint = <&display_out>;
>> +          };
>> +        };
>> +      };
>> +    };
>