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Date:   Thu, 29 Apr 2021 13:04:35 -0500
From:   Rob Herring <robh@kernel.org>
To:     Rajeev Nandan <rajeevny@codeaurora.org>
Cc:     dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org,
        freedreno@lists.freedesktop.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, robdclark@gmail.com,
        dianders@chromium.org, mkrishn@codeaurora.org,
        kalyan_t@codeaurora.org, hoegsberg@chromium.org,
        abhinavk@codeaurora.org, seanpaul@chromium.org
Subject: Re: [v3 1/2] dt-bindings: backlight: add DisplayPort aux backlight
Message-ID: <20210429180435.GA1385465@robh.at.kernel.org>
References: <1619416756-3533-1-git-send-email-rajeevny@codeaurora.org>
 <1619416756-3533-2-git-send-email-rajeevny@codeaurora.org>
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On Mon, Apr 26, 2021 at 11:29:15AM +0530, Rajeev Nandan wrote:
> Add bindings for DisplayPort aux backlight driver.
> 
> Changes in v2:
> - New
> 
> Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
> ---
>  .../bindings/leds/backlight/dp-aux-backlight.yaml  | 49 ++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml
> 
> diff --git a/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml
> new file mode 100644
> index 00000000..0fa8bf0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml
> @@ -0,0 +1,49 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/leds/backlight/dp-aux-backlight.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: DisplayPort aux backlight driver bindings
> +
> +maintainers:
> +  - Rajeev Nandan <rajeevny@codeaurora.org>
> +
> +description:
> +  Backlight driver to control the brightness over DisplayPort aux channel.
> +
> +allOf:
> +  - $ref: common.yaml#
> +
> +properties:
> +  compatible:
> +    const: dp-aux-backlight
> +
> +  ddc-i2c-bus:
> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description:
> +      A phandle to the system I2C controller connected to the DDC bus used
> +      for the DisplayPort AUX channel.
> +
> +  enable-gpios:
> +    maxItems: 1
> +    description: GPIO specifier for backlight enable pin.
> +
> +  max-brightness: true
> +
> +required:
> +  - compatible
> +  - ddc-i2c-bus
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    backlight {
> +        compatible = "dp-aux-backlight";
> +        ddc-i2c-bus = <&sn65dsi86_bridge>;
> +        enable-gpios = <&tlmm 12 GPIO_ACTIVE_HIGH>;

So the DDC bus is connected to a backlight and also a panel? This 
binding is not reflecting the h/w, but rather what you want for some 
driver.

There's only one thing here and that's an eDP panel which supports 
backlight control via DP aux channel. You can figure all that out from 
the panel's compatible and/or reading the EDID. 

You might also be interested in this thread:

https://lore.kernel.org/lkml/YIKsDtjcIHGNvW0u@orome.fritz.box/

Rob