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

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Date:   Fri, 13 Mar 2020 16:17:13 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Phong LE <ple@...libre.com>, 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

Hi Neil,

On Fri, Mar 13, 2020 at 03:12:13PM +0100, Neil Armstrong wrote:
> On 13/03/2020 14:40, Laurent Pinchart wrote:
> > 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.

How about replacing this property by bus-width to report the connected
bus width ? It should then become an endpoint property.

> >> +
> >> +  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>;
> >> +          };
> >> +        };
> >> +      };
> >> +    };

-- 
Regards,

Laurent Pinchart