linux-kernel - Re: [PATCH 1/6] dt-bindings: drm/panel: simple: Add no-hpd property

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Message-ID: <20181025175118.GJ154160@art_vandelay>
Date:   Thu, 25 Oct 2018 14:06:22 -0400
From:   Sean Paul <sean@...rly.run>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Sean Paul <seanpaul@...omium.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Sandeep Panda <spanda@...eaurora.org>,
        linux-arm-msm@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        jsanka@...eaurora.org, ryandcase@...omium.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Rob Herring <robh+dt@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/6] dt-bindings: drm/panel: simple: Add no-hpd property

On Mon, Oct 22, 2018 at 01:46:34PM -0700, Douglas Anderson wrote:
> Some eDP panels that are designed to be always connected to a board
> use their HPD signal to signal that they've finished powering on and
> they're ready to be talked to.
> 
> However, for various reasons it's possible that the HPD signal from
> the panel isn't actually hooked up.  In the case where the HPD isn't
> hooked up you can look at the timing diagram on the panel datasheet
> and insert a delay for the maximum amount of time that the HPD might
> take to come up.
> 
> Let's add a property in the device tree for this concept.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: Sean Paul <sean@...rly.run>

> ---
> 
>  .../devicetree/bindings/display/panel/simple-panel.txt         | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/panel/simple-panel.txt b/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> index 45a457ad38f0..b2b872c710f2 100644
> --- a/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> +++ b/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> @@ -11,6 +11,9 @@ Optional properties:
>  - ddc-i2c-bus: phandle of an I2C controller used for DDC EDID probing
>  - enable-gpios: GPIO pin to enable or disable the panel
>  - backlight: phandle of the backlight device attached to the panel
> +- no-hpd: This panel is supposed to communicate that it's ready via HPD
> +  (hot plug detect) signal, but the signal isn't hooked up so we should
> +  hardcode the max delay from the panel spec when powering up the panel.
>  
>  Example:
>  
> -- 
> 2.19.1.568.g152ad8e336-goog
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS